Best information on budget builds is in magazine articles. Here are a few:
1. Four-Grand Cadoo. Hot Rod September 1998
2. Big Daddy Caddy. Street Thunder January/February 2008
3. Torque Pig. Hot Rod July 2000.
4.
https://www.motortrend.com/how-to/hrdp-0804-541-big-block-cadillac-v8/
5.
https://www.powernationtv.com/episode/HP2012-03/the-caddy-500-other-engine-build-up
6. Hot Rod's 500 Chevette series. Someone help me out with that one, or others.
Best book (you will have to find it used) Big Inch Cadillac by Doc Frohmader. Try ebay.
Youtube
Best horsepower increase is with a cam, but that goes hand in hand with valve springs and rockers. Stock rockers are limited to about 4500 rpm.
Cheap horsepower with a thick spacer under the carburetor and a big air cleaner.
Upsizing the valves (especially to the intake valves).
Porting.
Edelbrock manifold (could require some prep or improvements)
Headers/exhaust
Turbo or supercharging is an option, see youtube with Richard Holdener Cadillac.
Search the archives on this website. A good chunk of the knowledge happened in the 2000 to 2012 time frame.
You never mentioned your intended gear ratio, weight, and how it will be used.
