This is the first I have heard of the QA1 unit being weak and/or flimsy. Can you expound on this please? I have the QA1 K member and suspension pencilled out for my build.
The QA1 K frame is not weak or flimsy. It weighs almost as much as a stock K frame, it's less than 8 lbs lighter. And it's much stiffer than an unreinforced stock K frame.
I suspect the OP thinks it's "weak and flimsy" simply because it looks like there's a lot less material- the tubes make it look like it isn't as strong as the wider/thicker looking stock K frame. But the stock K is basically just stamped sheet metal, and in unreinforced form it's pretty flexible.
A friend of mine has a QA1 K frame in his '67 Barracuda. It's a very well made piece. I wouldn't necessarily buy one just to replace an original K frame in good condition, I think reinforcing the stock K frame is probably the best bang for your buck. But if I needed a K frame, I'd buy the QA1 before I went looking for a stock replacement.
