Well the first thing youve gotta ask yourself is do you want to keep the car to basically the original spec or seriously modify it which is not favoured by the purists. Also how much have you to spend and how much hassle do you want?

A ZVH or 1900 CVH would be an interesting conversion but they wouldnt run on the twin coil setup without modification (getting a mappable ECU and setting it all up costs £££££s), or changeing to a dizzy setup with is inferior.

The next route would be to mod the 1.6 CVH, you could do lots to the CVH like Turbo it, get it bored to 1750 and run it on twin 40s but then the question of originality will come up as the twin coils would have to go, unless your willing to spend out on getting a mappable ECU installed.

Probrably the best thing to do is mod the original engine, get the bottom end rebuilt to basically standard spec, maybe lighten and balance the crank and flywheel. Get a stage three polished and ported head with an uprated cam like the CVH27 from kent cams, and fit a xr4i/capri 2.8 throttle body, this'll all run on the twin coils no problems and your looking at 130 plus BHP

This is basically the spec of mine, only to this im adding a Turbo Technics kit