I too have been header shopping & I've long been confused--many people on this forum state SD & SSAC are the "same". Yet, the primary/inlet are not the same size--SD ads I've seen are for 1.5" and SSAC ads are 1.75" The design/concept/install may be the same, but they advertise different inlet sizes....

SDs seem to hit ebay on and off, in past couple of monthes, I've seen highly rated sellers w/ buy-it-now prices for under $190 w/ free shipping.

SSAC has had same price, $175 + $50 s/h for at least a year. I have read numerous complaints about people not getting SSAC shipments timely, and no response from their customer sercive.