I understand, via Nial and a few others, that the Triumph and ?Lotus cars use the 3.75" centers, however, every other LBC uses 4" centers (which is actually 100.8mm exactly). 3.9" centers would equate to 99.06mm, so that is not true either. In fact, 100mm centers, used by GM cars, and a number of others listed under another topic somewhere, equate to 3.937." It is undecided whether or not those are useable, but one might be willing to take the risk.