If I can plant a seed...
Define what you want to use the car for and then that will kind of determine the general direction.
After that, there will likely be a short list of stuff that appeals to you either via brand loyalty or appreciation of some kind of technology or similar.
After that build the best car you can given the parts you can get at a price that you are comfortable.
Yeah, yeah, bunch of generalities.
In my case I like Chev V8s and had one lying around keep the sod behind the barn from floating away. In the end it will be too expensive to use it in a locost because to get what
I want out of a locost would require spending lots of money.
So my "fallback" became using other parts I am familiar with: Suzuki. Any engine that can spin an overloaded vehicle hauling a trailer for 6 hours on the highway, off-road in deep mud and goo all day the next day, including getting submerged and stalled due to water ingestion, then with a quick fluids change spin that overloaded vehicle and trailer back home another six hours at highway speeds and then do the commute to work the next morning without too much fuss is alright in my book.
Doesn't hurt that it is cheap, available, and very light either.