Thanks for the abundance of comments.  My primary conclusion is that I'm
sorry I asked :-)  

Seriously, I understand that 4130 is better, but SS can be used if build
sufficiently strong.  I had thought of aluminum, and since the engine mount
plate is already aluminum, it might not be so farfetched.  

I'll keep looking at my options, but I'd like to use angle, rather than
tubing if possible.  It would be more convenient, since I can bolt it all
together, and only weld where/if I need to. I'll use the same engine mounts
I used on the Kolb, and I'm afraid they might have been part of my problems
before.  If so, I'll have to change them, so I'm scheming to leave that part
of the mount bolted on, for easy replacement if needed. Bottom line is that
this is a big advantage of using the 304 SS, since it's widely available in
angle form.  

Thanks again,
Rusty