can anyone tell me why merc bellhousing dowel holes measure .725 to.680 and our on a taper. both bravo bells measure same with no wear. don't we need a good tight fit on gm's .625 dowels for coupler alignment?

They should be slightly larger.If you only had .001- 007 clearance on each pin,You would play hell trying to get the housing on or off,It would have to be perfectly parallel with the back of the block.You should not have any problems.If you think about it,when the motors running it shakes more than .050 .Put them on and go boating. JOHN

Johhnny,
I saw the same thing years ago.. I didnt like that much clearance. I added some copper material. Cant remember what.. I think it was copper tubbing or maybe a copper fitting for hard line.. Like the piece that connects two pieces of 1/2" copper tubing together. There are probably a million boats out there without it.. but if you do this to yours.. that would make two that do.

Just cut it off flush with the surface and bolt it on. They are still in there today. I have had my motor out many times and I dont see any ill effects from it.
Hope this helps!
Dick