I can remember going through all this too, I ended up grinding the 3 hex bolt heads and using a nylon button on a stock type (chrome) timing cover, as others have done. I always worried when I changed timing cover gaskets as some are thicker or thinner than the original set up one but it never seemed to cause any issue. I used an old stock timing cover with a hole in the appropriate place and a dial gauge to measure the play, this was a long long time ago and I can't remember the figure we were shooting for.
If you go to a Jesel belt drive you can set up the play / clearance much more accurately as they are supplied with a selection of shims IIRC. They are expensive but worth it in my opinion.