LMAO that would literally bring me close to vomiting. For the love of god please don't do that even as a joke lol.
So hey, in all seriousness though, if you really feel this way:
Then why are you still dead set on 20s, how did that become the magic number? I've heard a lot of people say that "oh there's not as many options available for smaller wheels, it's all about 20s now", but if the look you're going for is white letters, and 20s aren't offered with white letters, then it doesn't really matter that there are a hundred million tires to choose from that are 20s if none of them allow the look you want... If you want whites and can't get whites in 20s, how about 19s or 18s, hell even 17s? You're saying that you're afraid of spending 3 grad and ending up thinking it looks stupid, but honestly from whayt you say it probably is going to end up looking slightly more stupid than you hoped with 20s on it... I'm not saying "everyone must stay with 15s or 16.5s because the bible says so" lol, as nice as that would be, the only reason I like smaller wheels is because they allow the same "period correct" look that you also seem to like. But if the big wheels you were looking at won't even give you the look you were hoping for, then maybe you were wrong to think about 20s? I'm not trying to tell you what to do, but even your own post seems to contradict your supposed desire for 20s. Slightly smaller wheels will be cheaper, and have the potential to open up a lot more options for the look you want whereas the 20s ony offer different brands/tread designs that don't allow the look you want and cost a ton more. I'm not saying you must stick with 15" rallyes or anything like that, but it sure seems like you won't be as happy with 20s. Maybe don't get so dead set on that one size and just keep an open mind to what else is out there that you will enjoy on your truck.
You say you're building the truck for your kid, and who knows maybe your kid said "dad I want 20s", but seriously when I was 16/17 I wanted mirror tints, big flashy wheels, and blue racing buckets in my pickup. I was paying for most of it myself and asked for a few parts as birthday/christmas gifts or whatever, but thank god my father had good sense and said fcuk no to that type of stuff. Nothing wrong with going a little more modern but don't ruin the truck.
Also FWIW, I know a lot of people build trucks for their sons and that is super cool, I wish my dad had done that for me. But I also know I would have destroyed all the old man's work in the matter of a few months. We're talking about a teenager here, he's gonna do burnouts and jump it over stuff and spill drinks on the seats, etc. If you want to build a cool truck and let him drive it sometimes that's cool, but don't pour your soul and hard earned savings into a truck that you're just gonna turn over to a kid that will probably just put it in the ditch. Doesn't matter how well you raised him or how you hope he will act, young men are morons every last one of them, don't be shocked if he messes the thing up in a timely manner...