Is a 1983 buick regal frame the same as an 1986 monte carlo ss frame. I also thought it was a g-body but I am second guessing my self. I need a frame for my 86 monte carlo ss it was rotted out badly. I found an 83 regal and just want to be sure they are the same before I waste my time looking at it. Thanks

Dan

the frame is the same except for maybe the drivers side transmission mounting bracket.

it is a g-body and should fit. only thing that might need modification is the crossmember. on older chassis the cross member only mounted one way. on later chassis they put a second set of holes further back on driver's side for the 2004r. the th350 mounted diagonally while the 2004r mounted straight across if that makes sense

The G's with the 200R have frame extensions welded to the inside edges of the frame to mount the crossmember for the 200R. The G equipped with anything other than a 200R will need to have these frame extensions welded in. You could remove the extensions for your 86 frame and weld them to the older frame.
Bob