The main difference would theoretically lie in the timing curve as the later model was designed to match later engines
http://mgaguru.com/mgtech/ignition/pdf/ ... _specs.pdfthough in practice actual curve depends on the condition of the distributor innards, unless it is new or just checked/calibrated
http://mgaguru.com/mgtech/ignition/pdf/ ... s_dist.pdfdepending on level of tune you expect, the first step would be to check when advance starts increasing, when it reaches its maximum, and the static and max advance level. Once this setting optimal for your specific engine, if your are still not satisfied with the ignition curve, then the next step would be to start playing with the distributor mechanism, springs etc. or get it recurved from a known good place. Of course, ignition is only one part of a completely tuning an engine (everything being in good condition, it relies for instance on a good carburetion state of tune). Working with a rolling road or similar reliable reference may be required to fine tune to a level of detail difficult to feel otherwise.