When I dialed in the bell housing on my Champ 6 for the M5, I immediately drilled two new holes for 3/16 roll pins to hold the alignment temporarily. Then, as suggested in the shop manual, I enlarged two of the 3/8 bolt holes with an adjustable hand reamer set to 0.390"-0.3905". The "oversize" dowel bolts will then hold the housing to prevent it from rotating under load. Using a drill just makes the holes egg-shaped. I had been surprised how out of alignment the housing was with the non-original engine, but it was clear that the previous owner didn't address this.
Here's what the reamer looks like:
I doubt that the clamping force available from the other bolts in loose clearance holes and even a couple of small roll pins are enough to keep the centering of a bell housing under severe loads.
An adjustable ream of the correct size (4A) is not something that most of us have in a tool box. However, even the cheap Chinese ones are good enough to ream one bell housing and at about $8-$15, it's a small enough investment for one-time use. Here's one place to buy them:
http://www.wttool.com/category-exec/category_id/14710
[img=left]http://www.studegarage.com/images/gary_ash_m5_sm.jpg[/img=left] Gary Ash
Dartmouth, Mass.
'48 M5
'65 Wagonaire Commander
'63 Wagonaire Standard
web site at http://www.studegarage.com
Here's what the reamer looks like:

I doubt that the clamping force available from the other bolts in loose clearance holes and even a couple of small roll pins are enough to keep the centering of a bell housing under severe loads.
An adjustable ream of the correct size (4A) is not something that most of us have in a tool box. However, even the cheap Chinese ones are good enough to ream one bell housing and at about $8-$15, it's a small enough investment for one-time use. Here's one place to buy them:
http://www.wttool.com/category-exec/category_id/14710
[img=left]http://www.studegarage.com/images/gary_ash_m5_sm.jpg[/img=left] Gary Ash
Dartmouth, Mass.
'48 M5
'65 Wagonaire Commander
'63 Wagonaire Standard
web site at http://www.studegarage.com
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