Are these pistons any good: http://store.summitracing.com/partde...0&autoview=sku

I can only tell a 1cc difference and a weight difference (plus $100) between this one: http://store.summitracing.com/partde...0&autoview=sku

I emailed summit but they didn't know anything besides maybe the one that is cheaper was more popular causing the per unit to drop. I'm trying to get my compression down to 9:1 so's I can use regular gas. Also, is a onepiece rear main seal externally or internally balanced? Pretty sure it was internal.

I got vortec heads and I was wondering if the exhaust manifolds off my 305 would fit?

TIA