I have tried every penitrating fluid, viscrips and have only made myself frustrted. The air tubes on the manifold of my SB 305 are rusted on solid. Can I cut the **** coming from the manifold bushing and weld the hole up with them still bolted up to motor without damaging anything internally on the engine? FYI not concerned about putting new air system back on so I want them plugged ither way.

 

I'd suggest removing them. If a drop of welding slag were to fall into the header and bounce toward that valve, that could be catastrophic to your valves, heads, cylinder walls, and pistons.

 

Ya that's exactly what I was worried about I had just seen a few posts saying they left them on seemed odd considering the chances of that happening. Thank you for your time 1

 

You can leave a length of pipe sticking out, bend it over atleast 60* , crush the end together flat and braze/weld

 

I had the same problem. I ended up taking the manifolds off and soaking them in some of that WD40 rust bath stuff over night. Then they came out with vice grips...after the fittings rounded off with the wrenches. Then plugged them with brass block off fittings and re-installed with new gaskets. Then just cut the tubes off of the cats and welded the holes shut. A little more work, but better than having to look at those things under the hood.