I am using these 1 1/2" long bellhousing dowel pins from Summit in my Mega block with no modifications to pins or block.They had a good press fit and tapped in easily and smoothly.After checking crank/trans run out only had .003" so no offset dowels needed, just extra long. Summits filled the bill.
https://www.summitracing.com/parts/sum-192002 Bill