Not really an answer to your question, but I have managed to use an S10 frame (and engine) under an MGA ... my only issue was motor alignment in the engine compartment ... had to move the motor back 16" and down 5" from it's previous location.

I was thinking of using a Blazer frame, but the one I looked at had 4WD. A 4WD MGA just wasn't what I was looking for.