6.0 LQ9 4L65E swap 71 GMC 2500
 

My son and I are restoring a 71 GMC 2500 and swapping a 6.0 LQ9 with a 4L65E. Today we stabbed in the engine and transmission into the chassis for a test fit prior to removing for media blasting. We fitted the engine plates and mounts onto the stock perches. It looks like we are going to have to move the engine further rearward on the plates as we are having difficulty clearing the perches with the passenger side header. There is an approximate 1/16” clearance of the passenger side perch. The engine angle and transmission appear to be approximately 2.5-3 degrees so I think we are good. The long tube headers will necessitate either fabricating a new transmission crossmember or purchase one with provisions for a 3” exhaust clearance. What trans crossmembers are you guys/girls running to facilitate clearance for a 3” exhaust? Attached are photos of the build.

Re: 6.0 LQ9 4L65E swap 71 GMC 2500
 

I built my own crossmember but its similar to the store bought ones..except mine is double tubes...why 3in exhaust?

Re: 6.0 LQ9 4L65E swap 71 GMC 2500
 

That’s a nice fab job! I wish I had a tubing bender. My headers have 2 3/4” collectors but I say 3” because I would like some wiggle room and the collectors are pretty close to the trans crossmember. We initially have plans to have a drivers side inside frame fuel tank. After exiting past/ through the crossmember the drivers side exhaust will bend 90 degrees and route side by side into a two into one muffler.

Re: 6.0 LQ9 4L65E swap 71 GMC 2500
 

I wouldn't move the engine back too far without the cab in place to check firewall clearance. Are those Speed Engineering headers? You could clearance the engine mount bracket to gain a little room.

Re: 6.0 LQ9 4L65E swap 71 GMC 2500
 

I just fabbed up a crossmember, it's pretty easy. Just make sure you have the pinion angle where you want it and that the driveshaft has the right clearance through the other crossmember (allowing for suspension travel as well).

Re: 6.0 LQ9 4L65E swap 71 GMC 2500
 

We actually ended up going with an aftermarket Trans mount and I had to fab up a mount spacer to get the pin in angle correct tor the drivelines. Moved the engine mount farther forward as well. Seems to be coming along. It’s been slow progress since it’s a father /son project but we’re ramping up. Finishing up Brake lines and oil engine/trans cooler hoses and mounts for the oil coolers.