Do you have a front dizzy 1200 engine in the car, or the later [74 & on] A12 engine with the rearward mounted distributor?

Depending on your driving style, I would say that the 1000 radiator should handle a larger engine without difficulty. I do recomend however, that you have the radiator properly serviced, & if the core is at all suspect, then have it fitted with a new heavy duty core.
The 1000 radiator is bigger than the 1200 one & a heavy duty core will have more tubes & fins for a more efficient heat output. This is what I did with my radiator.

If your engine is a later type A12, then the distributor should fit right in, but you will need the steel mounting plate from a later engine if the dizzy is coming from the earlier 1200 engine.

The 1200/A12 flywheel is lighter than the ones on bigger engines & allow the engine to spin up faster, but not necessarily to rev higher.