Hi Tony,
The 23 & 25 were early siblings, with the 23 being centrifugal only and the 25 adding vacuum advance. Those distributors were replaced by the 43 (centrifugal) and 45 (vacuum) sometime in the mid-late 1970's.
The mounting shank is dimensionally the same, so the 23/25 and 43/45 distributors can be interchanged in terms of fitting in the hole. However, the drives changed as required for the application. The drive could be an offset dog (907) or a gear (Twink), and the gear teeth size and number could vary as required to fit different engines. If your distributors all have the same drives, then they can be interchanged in terms of mechanical fit.
Even if they fit, they can still be functionally set-up differently. The amount of total advance provided, how fast the mechanical advance comes in, and whether the vacuum provides advance or retard are all settings that can be tuned per the application. Just because it fits in the engine doesn't mean it works the same.
The dispatch number engraved on the side of the distributor body (like, 41584 for a 907) identifies that particular unit's application... if you have the directory of dispatch numbers... I don't. If two distributor's dispatch numbers are different, then there's some detail difference between them, either major or minor.
Any good distributor shop can re-configure your distributor to any drive or advance curve you specify. Advance Distributors in Shakopee, MN will rebuild a Lucas distributor to like new condition and re-curve it as you wish for around UD$125. Jeff Schlemmer,
[email protected]The head & distributor cap are smaller on the 23/25 and larger on the 43/45. Tiny caps with closely spaced high-tension terminals can only handle so much coil voltage before they arc between the terminals. If you intend to use a high performance coil, then the slightly larger 43/45 distributors are a better choice. But neither Lucas distributor is truly large, so neither is really appropriate for killer-hot coils. Hit them with enough voltage and they will cross-talk between the terminals.
Regards,
Tim Engel
Lotus Owners Oftha North (LOON)