There are literally hundreds of 948's knocking around so it'd be much easier to source one than mess with that one thats in.. if its original, it will be an 803cc which are fetching good money now even for rebuild, crank is a major weak point but other than that any inline A series is a drop in.
I restored my grandads A30 when i was younger and did the usual 1275 swap (used a Marina in mine) disk brakes, midget rear end etc:
Edited by cool_stu, 27 November 2015 - 01:53 PM.