There is a guy that races enduros here on the east coast that likes to tinker with projects. Last year, he rode what I thought was a 88/89 KX250. When I talked to him about it I found out it was an 87 with a 88 subframe and plastics. So, if you could put the bodywork and subframe, probably the airbox too, on your 1 year 87, you could possibly do the 89-94 KDX tank conversion. I did a similar swap with my 02 YZ426, I put a subframe, airbox and body work on it from a 2004 WR450. It was almost a bolt on and looked like it came that way.