Indeed Pilkie. If it aint broke dont fix it. I also believe in keeping things original. In this case I had a 10.5:1 lump, needing a cam shaft, carb rebuild ec. It had reached a point where it needed getting at. So I just went the efi route as a twin plenum sd1 at reasonable money made good driving sense. Used the engine and 5 speed box and broke the rest up. Engine stands in very reasonable money.
I just sold a 1973 3500S on the L, with the slightly lower compression lump, which had been retarded for standard unleaded + valvemaster. This drove really well until you nailed it. In fact it hated super unleaded, prefering std u/l. My Dolly Sprint hated unleaded more than any car I have driven, It got sold about 2 years ago now, but I was lucky to have a pertol station that still did leaded 4 star, which it liked. I have had eary Minis that burn out on unleaded ... as a matter of course I go and buy 2 cannisters of 4 star before attempting to start any old mini resto that has been laid up for many years. My Cooper is 5 star and hates u/l, as with my Dolly, all journeys are calculated with getting back to the 4 star station in mind. If a car runs OK on it, then fine. If your car runs sick on unleaded, pinks, has pre-ignition because of the filthy u/l, does valve seats and head gaskets as the u/l burns so hot, then you have trouble. Quite simply you are either lucky or unlucky. If your car hates it, then you need to have a plan. Loads of P6's have SD1 heads fitted, many A series engines have u/l heads, some have had valve seats hardened. To mindlessly say old cars run happily on u/l is simply not true. Some can run OK, some have trouble, but none of them will perform like they did when they guzzled 5 star leaded back in 1972!
As for having a brain in the car now, you are right, time will tell (ps its in the passengers footwell, cut into that honeycomb foot rest thingy whatsit
). I have read articles from the SD1 circles and it can be a pain in the neck. Again, it is down to luck and I will have to see what happens. But again, points are a nightmare, crap aftermarket condensers, old carbs going out of tune, pinking, dripping rope seals. Its 6 of 1 and 1/2 dozen of another. One good thing is, although we disagree, we both are out there bustling past Clios, BMW,s and all tht Euro tosh in a P6. Any presence on the road is a good thing for the marque .... however a more modern engine can mean a car becomes more driveable, will start every morning in the cold, runs more efficiently, plus an addition 50 bhp is not to be sneezed at, as well as a 5 speed box on the motorway.