Well, in the absence of any other suggestions except Jacques', I went with map 377.
Went very easily after that, uploaded the base map, and let it do the IAC, and that was that.
Would someone who's done this be kind enough to answer a couple of simple questions?
1) After the IAC has been autocorrected, the instructions tell you to manually align the blocks before and after the autocorrected ones, to make them a straight line to the first, and after the last, autocorrected blocks. Mine seemed fine already, not needing touched (although that screen, and hence the dots, is very small so it's hard to tell!) - is that normal, and acceptable?
2) I assume that's it, and (having checked that it's all set to closed loop) I just ride and let it tune? If map 377 was far enough off though, I assume that it will take a few miles to get things right, because of the 5% (session) learning, but the 20% (max) learning will get it there in the end?
Cheers,

Jim