12A Rebuild. Early Type Housing vs Later Model?
 

Working on a 12A rebuild. A brand new 12A housing (milled down GSLSE housing) is about $2000, brand new early 12A Housings are only $400? Can they be mixed/ matched? Or is the Trochoid shape different?

If your speaking of the dual dizzy early housing, then they won't work. The early ones have one less through bolt. You need 1979-1985. I think if you use the 1979-1980, they might have some small differences but will work.

I'd either find nice used ones or build a four port 13B with 12A irons.

This is a good reference. https://www.mazdatrix.com/b1.htm