I am about to start the swap and was checking how every thing was going to line up, and found that the header won't seat because of the a/c lines. I took the adapter off my third gen compressor and put it on the lt1 compressor and the header fit. So I was wondering if it is ok to use the that fitting on the new compressor . And if i can, do I still have to knotch cross member and cut the motor mount.

 

I'm sorry but I have no clue what your problem is. The header won't seat? what are you trying to do? You can't use either of the factory a/c line connections for the compressor. If you keep the 4th gen compressor, you WILL have to clearance the crossmember.

 

the a/c lines coming off the lt1s compressor got in the way of the first tube of the header. I got to looking and the lines off the my original compressor went directly to the left (when looking at the front of the motor) where as the lt1's lines off the compressor went back a few inches and went up (were it got in the way of the header) then to the left then back down where it turned under the compressor. Where the aluminum lines bolt up on the compressor look exacty the same only one uses a 12mm and the other uses a 13mm. Why would it not work?

 

got to looking it over again there is a difference how they seal but why couldn't i find a rubber washer or something. If i could get it to work I think i could reach the condenser and only have to worry about the hose to the evaporator

 

Try dropping the engine in with the compressor and the hoses hooked up and you will destroy the a/c lines on the crossmember when you pinch them between the frame and the compressor. You might be able to heat up the lines and bend them away to clear the header, but if you're not careful you'll snap them right off.