Small Block Chevrolet. V8 family starting in 1955 with 265 ci, up to 400 ci. GM updated the engine in 1987 by adding a new, non-split rear main seal (around the crankshaft at the flywheel) and provisions for a roller-lifter cam that eliminated the need for high-zinc oil, since the cam lobes did not rub on the lifters, but rolled across them. The next major change was the 'vortec' style heads that had really good flow but changed the intake bolt pattern and seals. There was a 'Gen 2' SBC that significantly changed the ignition and induction systems, but those are not common in the yards anymore.
If you must go with an LS engine, there are a similar variety of displacements, and they can be iron (trucks, generally) blocks or aluminum (performance cars, generally). It's a much more involved swap.
Transmission is the next thing to go - at $4 a gallon in the People's Republic, when replacing your blown up 3-speed, go with an overdrive, 200-4R or 700-R4 are the easiest to swap, but mods are required to make them work. If you go LS, just use a later automatic, potentially from the same donor car. Computer already set up for it.
Here is the EROD solution:
https://www.summitracing.com/parts/nal-19370414/
You'll need pulleys, accessories, motor mount adapter plates, lots of stuff.
If you're on a budget, stick with what you have for now. Odds are, it's a 305 (5th digit on the VIN tag is U for 1978). If it's an L, oh crap, you've scored, it was built with a 350. Let us know what you find.