Okay, long story short, I found 2 bad pistons in my 3100 hybrid, probably plugs too hot and clogged injectors, on #1 and #4. Spent the last month buying and fixing up a bone stock 3.1, replacing all the freeze plugs, buying and installing 2.8 fuel rail/cold start injection, adapting 1987 Camaro 2.8 harness to electric VSS in trans and manual reverse switch with 3.1 IAC, TPS, and oil pressure unit, replacing exhaust manifold gaskets (still have a broken bolt in #5 that WILL NOT drill out!), and swapping over manual trans parts.

Question:

I have the Walker 46669 350 2.75" intermediate pipe running to the back of my car. BONE STOCK exhaust manifolds on engine (going to permanently plug that blasted AIR tube port in the pass side exhaust manifold!), bone stock y-pipe with bone stock catalytic converter attached. Am I going to have problems attaching the converter flange to my intermediate pipe flange? If I have to separate the converter that's on the crossover, I'll have to cut it, and I'll have to cut the adapter on the cat that's still attached to the intermediate pipe (exhaust hasn't been touched except to disconnect crossover pipe from headers on bad engine). I'd rather not have to replace that adapter on the Magnaflow cat and have a cat sitting around which is useless.