if you wana lower your compression to suit the supercharger, 2 ways u can do it decompression plate and 2 head gaskets, cheap way to do it, the other way is dished pistons, don't plane the head, or run flat top pistons with the chambers in the head dremeld out, thats a far beter way to do it, its what i did with the head on my mini when i turbo'd it, the other thing is use a single 2inch su, hif44, you can get needles from mini spares in the uk or aus that they have that suit the carbs it might be easyer to start with 1 then can make your own fro there cos it will neva be right ether to lean or to rich, def beter have it a lil to rich.
locking your dizzy isnt that bad u just have to retard you timing slightly, ive owned alot of old skol minis and the same shit has been done with them over and over again, and just finished a 10g rebuild of a 1034cc turbo engine and done all the things you have done. cheers hope some of this info helps