om616.912 rebuild dilemmas

[rydzio]

Hello

I had a very embarrassing thing happen the other day.
I stripped most of my head bolts while unscrewing them. Please don't ask how
Fortunately they all came out but are not reusable.

The FSM says that starting February 1979 the head bolts were changed from hex to 12-point ones. The new ones are waisted and stretch when torquing. To account for the permanent stretch of the new type of bolts the bolt itself is 1mm shorter and the tapped holes in the crankcase have been lengthened.

My engine is the newer version after a power upgrade from 65 to 72 HP.
The problem is that it had hex head bolts

This doesn't make sense. It has the upgraded camshaft with longer stroke, chrome plated valve cap nuts, hardened lifters, hardened washers but the bolts are hex which would suggest that it's an older 65HP head.

Which bolts should I use? Hex or 12-point?
The FSM strictly says that on heads that came with hex bolts you should not use 12-point ones.

My concerns:
- The bolts changed in February 1979 but the power upgrade took place in August 1978 so I still could have the older hex bolts but an upgraded head (I think my engine number rules that out though - it's too high)
- My engine number is 616 912 10 093507 and this is way after the power upgrade of 1978. The upgraded engines start from 616 912 10 064618.
- Part websites say that the new 12-point bolts are for engines from 616 912 10 079811 - this would suggest i should use 12-point ones
- Head bolts might have been changed in the past from 12-point to hex by a butcher-mechanic
- Engine number might have been changed - probably starting to get paranoid
- I can't use the hex ones that came with it because I stripped most of them
- It is much easier to get the 12-point bolts (i have a set of goetze ones right now)
- I have not yet found anyone who sells the old hex bolts

Please help