Why are there so few blown small blocks?

The intake is a Weiand 7503 that I modified for the Magnuson supercharger. The pieces between the heads and headers are adapters that I designed and machined to fit the 302-351 Ford headers I'm running. Somewhere I have the manufacturer name for the headers but they are very well made, stainless headers with thick flanges and tube wall section that I picked up off of eBay for $200 (brand new).
Sure wish someone would come up with that for the LA motors for a less expensive header that would fit.