Thanks!
Unfortunately, it looks like this engine is off the table. I pulled the plugs and filled the cylinders with penetrant, but even with a breaker bar on both the crank bolt and the accessory drive, it wouldn’t even budge. I got curious and pulled a head, and sure enough it looks like the pistons are seized in the cylinders from rust. I tried knocking one loose with a couple whacks from a 5lb hammer just out of curiosity, but even then it didn’t help! To make it worse, I found the TV cable to the transmission wasn’t connected to the aftermarket carb, so there’s a chance that the transmission needs to be gone through as well.
However, the floor mat cleaned up well and further improved the interior, so that’s nice!