The bolts in the end of the head are either 8mm or 10mm depending on which version of the 2.9 you have.
Correct, there is some difference in accessory bracket bolts.
Does anyone know if there is a significant difference between the two enginse other than the bolt sizes. I need an engine for my 1989 bronco 2 , the engine i currently have has the 8mm head bolts and the only engine that I can find is the 10mm version. Are all the accessories as far as ac and the like interchangeable between the two motors ?
I've been through both head setups on my 2.9s. Never noticed a fitment difference, and as far as the bolts went, I replaced mine with 10mm when I installed my HD heads.
If it were me, I would be more inclined to use a 10mm version - accessory bracket holes were changed for the 89TM heads, which are superior to early 86TM heads. 86TM had the 8mm bolts, and are also the heads that are more inclined to break.
What went wrong on yours? The bottom end of Cologne engines are very stout, and have forged cranks and rods in the RBV versions. If it was just a broken head, ProMaxx makes a damn fine head, reminiscent of the World Products ones.