I'm trying to remember from my busch pressman days...
You can get a little more extention by filing off the extention stopper.
As said above, the plate that attaches the bellows to the front standard can be widened to allow for larger elements. I think the max un-altered is 57mm. A 90mm f8 super angulon will fit barely. a 210mm symmar-s (the later versions) will not fit. The 210mm symmar convertible and the 210mm sironar should fit.
The front standard may not be very stiff. I had to dissasemble mine, add a shim under the pressure plate, and reassemble making sure everything is tight.
The kalart rangefinder can be adjusted to any lens. check out graflex.org for instuctions.
the lensboards can be very hard to find or very expensive.