If you run a 109 (86-87) block, there is a threaded hole in the front of the block, just above and left of the timing cover. If not using it, you should be able to plug it. If I remember correctly it is 1/2" NPT? So, find a brass plug for it. The 85 block has a different deck height, but you need to search, or someone will post up the difference. I forget... Cranks are the same either block, so are rods and heads. Unsure about pistons, its been a long day...
Also, some 85 hot air blocks are 20 bolt, which means your pan will fit on the 109 block. If an earlier 85, you might have a 14 bolt pan.
