Ignition upgrade, which one??

[Grunter]

I was all set to purchase the aldon electronic ignition upgrade for my 3.5 carb R/R which is currently running a lucas sport coil, however once again the goalposts have moved!! I run LPG most of the time and have been looking at these timing processors available, and theres where the confusion starts, the two units i am thinking of are the A&R amp by RPI or the one by chris perfect, as far as i can gather one has an analog retard adjustment and the other has a number of selectable positions but a greater range, is this correct? Then there is the issue of compatability, will either work with the aldon ignition? (or any other aftermarket electronic ignition) is the lucas coil compatable?  

any info to save me the headache of a mis-matched system would be great.

[Range Rover Blues]

I'm a bit dubious about the Iwema one now I've got it, it plays up regularlt and I've been told there are others available at half the price.  That said it works with the factory electronic ignition system, why no hunt one of these down and then you have a stcok system.