If your car is a 988cc manual...then this carb will "run the engine" fine...
the risk is that the electrical connectors and throttle cable connection & airpan cable support brackets may not be the same as on your J reg.
your J reg will surely have a modern throttle cable attachment (adjusting nuts on a screw thread atached to the cable assembly. the matching holder for this on a J reg carb is a "fork" on the carb......earlier models of throttle cable comprise a simple collar on the cable assembly...and the matching part on the carb for these is a "clamp" that is used for adjustment.
similar story for the electrix....
your J reg will have chunky gray connectors (oval) with a rubber seal inside that clip together and can be mounted on the modern air filter housing.....the earlier car wiring and carbs used white translucent rectangular connectors that just pushed together and dangled (and were subject to vibration).....so these could be different..
I have a C reg with the old style and a K reg with the new style....the burning question is ...
Does anyone know at which point the new interfaces were brought in???
if its earlier than this E reg then you could be on to a winner...if its later then get ready for a super bodge...(or avoid alltogether)