I think that you are right about changing the adjustment method for a race or track car. Most circle track cars use adjustable A-arms.
Years ago I saw a magazine article where a street rod builder was using MII front components, but changed the adjustment method. Instead of the UCA cross arm mounting to the horizontal top of the spring tower and adjusting via slots, he turned the mount 90 degrees to vertical and used shims to set the alignment. The trick would be to weld the correct grade of steel angle bracket to the right place on the spring tower, drill it properly, and brace it as needed.
I've seen the adjustable UCA's in a couple of places, but can't come up with them right now. I thought that Speedway Motors had them, but no.