The head will physically bolt on, but it will be a little anaemic, the 144/170/xp-xt 200 have smaller valve sizes, smaller combustion chamber (will raise compression) and a smaller carb flange, you could put one on to get by but you will need an earlier carb to suit the head, you can come into issues with pushrods though as most of the earlier engine have a solid cam not a hydraulic, you'd have to use you 250 rocker gear and maybe have to get aftermarket pushrods to suit, you will need the earlier rocker cover too, as far as I know 221 head is interchangeable with a xy-xb 200 & 250
Thanks for the info.
Sounds like a can of worms that I hope can be avoided
Repco has got me some HIGH TEMP JB WELD which I hope will do the trick.
