I've just bought a Mini to restore and it has a Cooper s front disc brakes and Hardy Spicer drive shafts. The car didn't have a engine but a found a 998 cc engine with rubber cross drive system. Should I buy the parts to fit Hardy Spicer flange to the diff or convert it to a Pot Shaft drive..

Well the splines on the S driveshafts you have will also take the rubber joint yoke.
But I'd not do this as the rubber U/Js are rubbish now.
Most folks go for pot joints- they give less power loss than H/S joints, and the parts are much cheaper.
You will need to pull the diff out, fit pot joint diff shafts, and swap your driveshafts for pot joint ones.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

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