A little follow up about head locating dowels.
I have three 1500 engines torn down at the moment; a '79 carb version (with M12 hardware), a '80 FI, and a '85 FI (both with M10 hardware). All are 10 bolt heads. I discovered the '79 has the shorter dowels, while the other two have the longer ones. So despite all three being 1500 blocks, there is a difference. Perhaps the dowel length is related to hardware size more than block displacement? Or it might just be one of those variable things with Fiats.
As it has been noted, the blocks have different depths of recess to accomodate for the length of the dowel ('79 has shallower recesses). All of the heads have the same depth of recesses. Another odd finding was the short dowels in the '79 were extremely brittle and fell apart (crumbled) upon removal (this engine appears to have never been opened before). The longer ones in the other engines did not.
No significance to any of this, just passing along what I've found.