First off, you communicate extremely well for someone so young. Your thoughts are well-organized, and you seem to have a methodical approach. These attributes will serve you well.
Second, there's a big gift there from Robbie if you can arrange transportation. By all means, take advantage of that.
Third, yes, the Ford S-Cort (getting around the word filter here) was hugely popular in GB, and made sense as a cheap donor car when the book was written, but it has since gained in value due to its race/rally heritage. Equivalent products here would have been Ford Pinto, Chevy Chevette (also popular in GB), various Datsuns, RWD Corolla, etc - any cheap RWD four-cylinder economy car of the 70s and 80s. That was a long time ago now. Despite the fact that I am more familiar with Toyota stuff than anything else, it's really hard to argue with a Miata as a donor car.
Third and a half, I'd way rather use a Miata powertrain than any S10. A great big wheezy greazy cast-iron truck engine is the exact opposite of what you want for a flyweight sports car. There is nothing sporting about them. Sure, you can find parts anywhere, and maybe even some go-faster stuff at Summit or Jeg's or whatever, but it's a heavy, slow-revving truck engine, and does not have a sporting character. Leave the 4.3 to what it is good at (e.g. towing trailers full of yard waste to the dump, reposessing TVs and odd-smelling sectional couches from sketchy rent-to-own outlets, taking Grandpa fishing, etc.) and stick with small-displacement, quick-revving engines for your Locost.
Honestly, I'd rather have a stock 3T-C with a lightweight flywheel than a big old asthmatic V6 making twice the power. A small, fast-revving four-cylinder will result in a much better balanced car that will be more engaging and will feel much faster, even if it's not actually faster around a track.
Fourth, steel tubing typically comes in 20' sticks from a steel yard. If you have one nearby, it's worth pricing it out. The ones I have bought from have been happy to cut it into 10' sticks at no charge, which made it easy to transport in a longbed pickup. It's not free, but it's not an expensive material, and it's easy to work with. I like my 4x6 bandsaw, but you can cut it easily enough with a porta-band, or a grinder and cutoff wheel, or even just a hacksaw if that's what you have. And it's forgiving to weld with if you use MIG (as opposed to stick or fluxcore). Keep your gaps reasonable and clean the metal prior to welding, and you'll learn quickly.
Good luck. I wish I'd have had the opportunity to do something this ambitious when I was a pup.
