The gibs themselves don't really vary any more than the rest of the machine does. What I meant was that the gibs ride along the bottom edge of the bed, and while this is a machined surface there doesn't seem to be a whole lot of QC involved when it comes down the the actual thickness of each & every set of ways. The most common problem that crops up when doing this is that the ways of the donor bed are from a different batch of castings and the ways are marginally thicker or thinner than the bed of the original lathe. If you're lucky the two beds will be very close in size and it's not an issue, otherwise there's going to be a step at the joint and the gib will catch on it. If the step isn't too bad you can run the gibs a little loose but that compromises accuracy and only gets you so far anyways. The best solution is to make the two even by either milling down or building up the outside edge of the bottom of the ways where the gibs ride. For some reason most of those I've talked to had donor beds that were thicker so it was a matter of milling or shaping the edge down a bit to match the original lathe. The only one I know of that had to build the area up did so with moglice and seemed happy enough with the results.
Dave
www.broncosaurus.net