Some things you will learn are:
Not the land of the free anymore and the home of over 1,500 government agencies that tell us what we can and cannot do, mostly cannot.
When you modify a vehicle and call your insurance company may find out your yearly premiums are only a few dollars more than than the amount of coverage they are giving you.
May learn there are over a million different connector configurations, its a lot easier to find a mate for yourself than trying to find a mate for one of you connectors.
Let me take you back to the 50's/60's when it was legal and insurance companies didn't care. Could by a clean say 48 Chevy coupe for around 50 bucks, no such thing as rust back then use to add nickel to the steel. Any wrecking yard would sell you a 57 Chevy 283 engine for 65 bucks, complete, you pulled it out yourself, Warshawsky would sell you an adapter plate and bolt on engine mounts for around 10-15 bucks. Manual transmission could handle this, today, made out of paper.
Ford was a bit better, used a torque tube for the rear differential, Chevy, had to add a couple of bolt on torque tubes so your rear different on leaf springs wouldn't twist. One fuel line to hook up to the engine, ha, even had a double flaring tool kit back then, still have it.
Headers were cheap, and with a frame, plenty of space to add dual exhaust, some used straight pipes, but depending upon where you lived was better to add a couple of glass mufflers for around five bucks a piece.
To get the thing running, just two wires, one for the ignition the other for the starter solenoid, push button on the dash, and whenever you pushed that button, starter would engage. But then we had brains not to push on it when the engine was running, no more brains left today.
Instrumentation, fuel gauge remained the same, speedometer had a cable to the transmission, didn't worry too much about the clutch, could replace that in about an hour for six bucks. Oil pressure gauge was a real oil pressure gauge, bit more tubing to fool with, ammeter was in series with the battery vehicle power cable, only the starter had a big fat wire. Not connectors, just ring terminals, some just wrapped the bare end of the wire around the terminal, sloppy. Having a mental block right now on the temperature gauge, but wasn't a problem to hook that up either.
A lot has changed since then, major motivation for us poor kids doing this is so we could leave spoiled brat rich kids in the dust, and that we did, but really don't know how to deal with the spoiled brat rich kids running out country today.
Ham about 20 years ago, one of my boys wanted a father and son project to build a kit car, I called over a dozen insurance companies back them, most of them wouldn't even provide coverage, others wanted more for premiums than the coverage. See a lot of this stuff on TV today, never talk about insurance, and for most states, is the law.
Back then, no radar, if you saw a cop and you could see them, would have to pull behind and clock you, if you were too stupid to slow down, you deserved that ticket. Today can go under an underpass and get a ticket in the mail. Also have spy boxes in our cars, can't lie about what caused an accident, the truth is in that box.
One key reason why I refuse to buy a vehicle without cruise control, carry a thermos full of coffee and constantly slap my face to stay awake. By the year 2000 we will be all driving at 300 mph, try more like 10 mph, many sections of our town are this way, wow, I can go 25 mph in some places! And 55 dang sure means 55, even got a ticket once for going 58. Was told the law is like a plate of glass, once broken, its broken.