i was always told that a stock RB block was good for about 600hp max(Safely) and the B block being good for maybe 100 more HP..now with that being said , i would use a main girdle and good main caps to hold the bottom together and then squeeze it for about 800-850hp..i never liked the hard block but as was mentioned above, everyone has their own preference and ideas..alot of guys are making 900+hp with a stock block, but i wouldnt chance all those good parts to a 30+ year old block.