Cheers chaps ,
I have the box sorted, i found a H150 and am in the process of fitting. My calculations tell me that fitting 4.1 diffs in place of the 4.3'swould put me back to almost the origional gearing of the R151, which is actualy quite good for the Hzzz motor.
I would, however only considder direct swaps which plug into the existing electrical system, hence my question.