Not certain what years will "fit", but, for what it is worth, I put a set of head pipes from a Twin Cam 88 on my '86 EGC. The head pipes bolted up with no problems, but your mufflers will not attach to the later head pipes.
1995 was the year the muffler/head pipes changed. Up to '94 the mufflers slipped INTO the head pipe, and had a collar. '95 up mufflers slip OVER the head pipe.