have just bought what i thought was a 79 xl 125 in bits, as usual it turns out its a 79 xl 100 s ! the engine i planned to fit was my from my old 125 r mono shock, think it was a 1985 ? will it fit ? have offered it up and will get the front mounts ok but the rear ones need a bit of fiddling with but i think it should go in. has anyone here done this or heard of it done ? am worried about the top mount on the head as it looks a bit tight lol. any help or advice greatly appreciated !