Big Cad into 78 thru 88 Gbody Cutlass, Regal, Monte Carlo, Grand Prix, Malibu, Le Mans, & El Camino
For motor mounts two L shaped brackets one side of L drilled for Cad motor mounts the other drilled or torched for your existing frame holes. You can make these out of 4 pieces flat stock or buy them from a vendor. I bought mine to save time and head scratching. Use thick stock she bent my first set. (Torque & traction will find the weakest link) I believe either Eldo or rear wheel drive mounts will work one may be a little lower or drill new holes in the side of the mounts to keep the motor even lower. Keeping the motor low is a benefit as it provides more hood clearance at air breather with aftermarket intakes and for the AC compressor if you decide to keep your Gbody AC, also optimum drive shaft angle, room at the AC box & center of gravity. Both of mine sat low square and back close to the firewall both just mounted to the factory 200-4R with no adjustments to the transmission mounting or driveshaft. If you use a th400 as most do you may have to cut your drive shaft depending on short or long tail and on what rear you choose i.e. factory 7.5, 8.5, a 12 bolt or ford 9. You will probably have to modify or buy an aftermarket cross member. I just heated and shaped mine for dual exhaust but you can now buy them ready made for reasonable money.
Use the 68 thru 76 Eldo oil pan, pick up tube, dipstick tube & dipstick. If you break the dipstick tube you can make another out of a common stick of 3/8" break line and compressions fittings. You can also buy one like this from MTS or CPP. The vendors also have aftermarket pans. FYI their is two holes in the block for dip sticks to go into. One being occupied by the dip stick tube the other by a common ball bearing. If you start with a rwd motor and add a Eldo pan you have to swap the ball bearing & dip stick tube otherwise your Eldo dip stick may catch the crank and get mangled or worse.
My first car had weak stock springs but even with the motor sitting low probably a little lower than the factory 307 sat I never hit the pan even when I bottomed her out. BTW engine weight 599lbs less if memory serves me 22lbs with the Edelbrock intake. So even with the weaker of the factory springs it handled decent with just factory F41 sway bars, 15x7 wheels, & 235/60s.
For practical purposes all 68 thru 76 472/500 blocks are the same. Again for practical purposes there are only two factory 472/500 heads early 68 thru 73 which is best for performance and say a 10-1 compression build or 74 thru 76 open chamber heads for a 9-1 or less build. At the back of the passenger side head is a coolant passage that most will have a fitting on that is too long for our firewall. I wanted to keep the coolant flowing thru the back of the head for optimum cooling so I got a short 90 degree elbow that would screw into the back of the head and another that will screw into it to mount the hose to. These are available at any plumbing supply Lowes or Home Depot. She has been detonation free as noted on a teardown in a true measured calculated 10-1 motor that was sometimes run on 89 octane. The combustion chamber in these heads were ahead of their time as they have a great heart shaped chamber much like the new Chevy LS1 motors and even have the same fireing order as the new motors. That’s not to say there isn’t hugh improvements in the new aluminum heads. Note you can also drill the back of the driver’s side head and put one there even though Cadillac did not. There are pics on the Cadillac power forums albums and I believe also on a link from the CPP website.
If you want to keep the Gbody AC you can easily do it with two brackets from an 80/81 Cadillac 368 as they used the newer style “pancake” compressor that we have on the gbody. I modified the brackets a bit so the back of the support bracket would bolt to my Edelbrock intake. The passenger side valve cover should fit snug up against the AC hamster wheel box if the motor is centered. What I did to provide more room so that I can take off the valve cover without unbolting a motor mount and jacking up the engine was to cut out the side of the hamster wheel box and move the wall back in ½” then fiberglass it back up and shoot her with a lil black spray paint. It was cheap easy & common sense with a small fiberglass kit from the local auto parts store and I had never fiber glassed anything before. Keeping the AC is nice in the heat, gets you props at the shows, and will get you a bigger market better price if you sell the car. Its not a small block the few pounds & lil drag of the AC won't make the big Cad any difference, like a diesel truck pulling a lawn mower trailer. If you are not building a stripped out drag car it makes no sense to rip out the AC IMO. On the drivers side again with the motor centered the exhaust manifold or header will be very close to the steering shaft. Both of mine fit without adjustment but both were center console cars not column shift. I made headers from BBChevy gbody headers and a Cadillac flange that you can get at any vendor. Up front I used an oil pump from the 77 to 84 425/368 as it tucks up closer to the block and provided more room so that I could run the larger sway bars without washer between the sway bar and the frame. Instead of using stock or even the large factory F41 bar I am used a 36mm hollow bar from an early 90s WS6 Trans Am. Also I have read that the Sanderson CAD600 shorty/mid length headers fit with minor adjustments.