Do it then let us know how it turns out.

 

If you're doing it correctly gas welding can be very strong, surely would hold up for exhaust & charge piping.

 

if you can weld outright strength wont be the problem. the problem with oxy-fuel welding is the insane amount of heat you put into the materials, which causes lots, and lots of warping. it'd be OK for building the exhaust no questions asked, i wouldn't use one for a manifold personally.