Allen headed bolts worked just fine. Just finished one this week. The real problem is clearance. I like .004 to.006 cam end play. I install the cam with button and gear in place and nothing else. Then I bolt on water pump housing with gaskets in place using a feeler gauge I find the clearance between back of housing and button. Measure thickness of timing cover then find a washer that when tack welded to cover will give the clearance I want. Aluminum cover will not flex but steel cover will flex a lot.