In my 77 REPU I puled out the old stock engine and dropped in a 13B from an 86 RX7. I gave it a street port and put a 36mm sidedraft webber carburator on it. I also put a racing clutch in it and still run the truck transmision. It all bolts together the same and didnt require any force getting it together.
Are you sure it is a 36mm sidedraft you put on? That sounds really small. I did the same thing as you but my motor isn't ported and I have a 48mm sidedraft carb. I think the hardest part of the job was finding an oil pan.
Did you figure out a way to run your OMP or do you just use an oil pre-mix? I went the pre-mix route but would love to hook up the OMP again and not have to worry about oil at the gas station.