Dude, that's amazing.
I'm glad there's at least one guy left in the USA who is keen on the much-maligned Buick Opel by Isuzu.
I actually bought one in 2011 out of Michigan, I think. It was an ex-Texas car that had been taken to Michigan by an enthusiast who had owned a Buick Opel sedan when he was younger.
He had the 1976-model trucked to Michigan, gave it a new interior and hoarded a bunch of bits from Australia... then decided he'd lost interest.
Well, that Buick Opel by Isuzu popped up on Craigslist AND Just A Car Geek and I bought it, shipped it to California, then shipped it to Australia.
It's not been registered yet; I have some other Isuzu projects on the go, plus a young family, but it's on the cards. The few times I have had it out, it's astounded and confused people; not because it's unfamiliar; being essentially the same shape and grille as the 1976-1977 'TC'-model Holden Gemini, it's still familiar to anyone older than 20 years old, but because it's SO familiar, yet left-hand-drive!
I think I would have preferred a later version, which had the Buick badging on the nose and steering wheel, but beggers can't be choosers, especially when I have seen how much work you've put into yours. I'm not overly mechanical; I'm into the history and I love driving them, I just don't have the time, patience nor skills to dick around with cars, but I'm glad someone like you has.
Good luck with the rest of the build; I've just read the thread from start to finish! Two long, hard years condensed into fifteen minutes!
Here's mine at a show here in South Australia a couple of years ago: