treiSHU said:either this one
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or you make one of these and you drill 4 holes into the diff and make a thread for the bolts. iirc there was one for sale on ebay a few months back.
Valver Box, with the weak circlip diff, and valver short ratios 50-80-100 (min average max)
Valver JB3 with bolt in diff, dunno, perhaps £160-180-200
Williams JC5 with longer 5th ratio 120-150-200
matteh has a spreadsheet with all the renault boxes and the ratios which you might find interesting.
edit: do you mean the reconditioning itself? I think I'm teaching you to suck eggs here arent I?
you can tap the casing to take the diff retainer plate, no need to swap diffs etc.
rebuild will typically cost £350.