Re: may be trading my regal for a monza...
Floor under drivers/passenger feet is a bad rust area. Check to see if the x-member is hitting the oil pan, these cars are known for bottoming out and the x-member bashing up into the pan. Is it a stock 4 speed set up (cable clutch)? The stick cars were known for the cable ripping wight through the firewall, extra bracing is recommended in this area. Most of the suspension and brakes were undersized for theses cars, so check all that for wear and tear. Master cylinders, brake Check the torque arm for damage, and make sure the bushing in it is good.boosters, and heater cores don't seem to last long in these cars either.
Also, if that's an original Monza TH350, note that it will have one less bolt hole in the bell housing.
And the torque arm bolts to the transmission tail sahft, so that will limit your choice of transmission. Unless you change the rear suspension setup.
If you go for it, start looking for armrests. They don't last long in these cars, and are hard to find.
If you ever do a V8 swap, new front coils is a MUST.
My first car was a 1979 Monza Spyder. I drove it off and on for close to 7 years. Was one of the funnest cars I've driven. When the suspension is good, they are a great handling car. But know this, you can't be nearly as rough on one of these as with a gbody. They break really easy. And with stock breaks, if it's a dd expect to change the pads once or twice a year. 2 years if your lucky on the front tires if you run stock 13s.