Yeah, It certainly seems like I would be pushing the blocks longevity and that a mega block would be strongly advised. I would like to ultimately go that route, it will just mean that I'll have to wait longer to do this buildup- I'd rather only have do it once though.
IMHO a megablock in cast iron will put a lot of weight on the front, making it very hard to hook. The traction difference for unpreped surfaces is huge!! Go aluminum, or at worst a low deck with a lowdeck sixpack, my opinion on this. If you are also going to have a less than optimal suspension, the situation snoballs some more.