Josh,
In my previous post, when I said that 0.3mm shimming was not an issue, I had inches in my head, as in 0.003" (which I then corrected to millimeters in the text but not in my head). Sorry for the confusion. The actual 0.012" of shim is, indeed, significant and makes me guess, (and it is just that, a guess) that the previous builder was trying to split the differnce of the total required shimming in order to place some on both sides of the crank. I can't recall exactly how much shimming I required, but I seem to recall it being more than 0.024". I will look for some note I may have made, then I would be able to give you a better answer on this.
It would be very interesting to know how much shimming was between the left-side crank web and the roller bearing. It would also be interesting to see what the bush landing looks like.
I never forget that there are plenty of members here with considerably more exerience than I and can probabaly cite, from memory, a working range for total shimming. Boys, jump in.
Richard L.