Having finally managed to get the shoes fitting nicely all the way around (using thinnest feeler gauge to check contact/high spots, i have finally got the whole thing back together, engine back in and re aligned and all seems good. As a bonus, having had the bearing housing at the forward end of the reduction box sleeved the whole plot runs much quieter that before. We are yet to venture out but having run in forward and reverse for a while, so far so good.
having to remove the reduction box (and therefore the engine) to lift the top half of the gear case off seems a bit daft as replacing the top 4 studs with bolts would solve this but perhaps there is a good reason for using studs rather than bolts!
Thanks for interest and advice, much appreciated. Fingers crossed for first trip out.