Aha, this is the engine you mentioned!
If Ford bearings are anything to go by, hopefully you should be able to get up to +40 which is around 1mm. I'm trying to get my head round how much needs to come off, but unless it's a 0.5mm flat spot on one side, it shouldn't need a whole mm. Fingers crossed on that one. Out of interest, do you know a reliable crank grinder?