Paul,
Given that your bush journal is now 0.0185" under standard, going with a -0.020" bush means you are limiting your machinist to about 0.0025" to 0.003" of meat to work with when boring the new bush to fit, assuming you don't grind the journal first (which, I think, amounts to about the same thing). This seems like a problem to me, but I am no master machinist (furthest from it, by other recent admissions). Now, supposing you go with a -0.030" two-part bush without grinding the journal, you will be removing a lot of the inner bush material, which also seems like a problem. My thinking is that a -0.030 solid, one-piece bush gives you the best opportunity to keep the journal as it is or grind it to clean-up only. Then, the bush can be bored and honed to a close fit.
EDITED: Now, here's the most important part: let's wait to hear from a few others before believing a word I've said.
Richard L.