Finally got the engine bolted in place. Not too tough, just took some trial and error with the DIY adapter plates.
Had to do some surgery on the old SBC mounts, as seen here:
and a better pic here:
It's tough to make out, but I had to trim it to clear the bolt. Nothing would line up without it. I also had to trim a bit to keep the mount from hitting the block, but a pic was impossible once i got it installed.
Don't have a lot of room for headers here:
Plenty of firewall clearance, though. And this is with the motor mounts in the back two holes.
Some tips for using the DIY adapter plates. Bolt them to the block and then the rubber to the adapter before you start dropping the motor in. Had a booger of a time tring to bolt them on the block once we set the engine in place. Wound up pulling the engine back out and bolting them down first. Hope it saves you some time. Also, I don't know the thickness of the plate, but I feel like a slightly smaller thickness would make this job a bit easier (can't speak to it being strong enough, though. Had a machinist in my family make mine and he used some scrap he had on hand).