Stock oil pan is way too deep. GM hotrod pan is ok in a stock ride height situation but still hangs below the crossmember. Loads of motor mount options. I've heard gto manifolds work if you wanted to go that way but I don't have firsthand experience.
That said, adapters are junk because they make setting your driveline angles a total b*tch as it raises the engine... and raises the trans up in the tunnel... leaving you with a downward angle at the tailshaft. Garbage!
Buy the Holley stuff, it is a well designed system. Save up if you need to.
Thanks for the replies I'm gathering info and it deffinately looks like the Holley mounts and oil pan are the right way to go. I was gonna do a stock bottom end ls but went ahead and bought forged rods and pistons. I'm looking for 450 to 500 go n/a with turbo in future. Was gonna be a budget build but that's hard to do on a budget I think.. any more info is appreciated thanks