FJ11/12 is same engine as xjr12/13. 2mm bore size increases between the 3 sizes. ignitions and carbs vary but otherwise mechanically identicle right down to the comp ratio until efi came along. some speculation over whether fj11 had a bigger/better cam but this just seems to be the UK spec cam, all us and aus models had identicle cams but UK had better breathing. heads, barrels and bottem ends all interchangable up to efi models.