I have a 76 Trans, that I bought new in Faitbanks Alaska, its a 4-speed with 2+2 seats factory chevy orange. The first thing I did was put N-50 on the rear and G-60 on the front, I never left the light not smoking the tires. I was then station at fort Bragg N.C.. where I blew the engine. When I left the Military in Feb 81, I towed my car back to Atlanta, where it sat until 84. I built a 455 Pontiac motor, no SD or ram air stuff. the motor was strong and a killer of mustangs bottom to top. In April 85 One day I tact the engine to 5000 RPM and dump the clutch, as a young man I then relized that there's a limit you can push a two bolt main not balance or blue printed motor. But the point I trying to make is go with the big block conversion, it not hard at all I now have a 402 chevy in my TA-rated at 470hp. The engine will fit under the hood, you will actually have more room to work on headers and with the steel motor mounts the engine will look factory. The only thing if you plan to use headers at the time I did my swap in 94 Hooker was the only headers that would accomandate the big block on F-bodies car. The only year GM but a big block in a F-body car was the 396 Camaro in 1969. But difinetly go for the swap its simple, cheaper HP, Parts are available.
Robert