There is more out there then v8s, 2JZ and SR20s
those have been done and over done, make great power, reliable and whatever.
Why not try to keep it mazda?
Depending on your power goals mazda has perfectly good engines that can make really good power. Many swap in with a bellhousing change.
That is what I am doing with my F2T powered FC.
Chances are mazda being a small company shared the same MZR block with some RWD mazda.
As things are I can bolt up an F2T, FE3 strait up to an FC, FD, Miata, or even an Rx8, at times even without a bellhousing swap.