I just bought a new Hitachi starter with the mounting pad for the GM stuff. Kragen/O'Rilieys sells them in the performance sections of the stores. It listed for $159 but I got it for $125 matching Summits equivilant, got a good deal on it in other words.
I know the mouting block/pad has holes only for straight mount which most small and big blocks have holes for both staggered and straight bolt patterns so you should be good to go here. Plus, it has 2 sets of hols for both styles of flexplates, small and large.
Pretty universal, bolted right up and needed no shimming either, very happy customer here
It just sounds like a Toyota when you are starting it, but I like that.