This may be a bit late to help you as you started this thread back in Feb. BUT; The C4 control has not been supported for about the last 7-8 years. There are numberous chips on the bord that are no longer made and no direct replacments are made. There is some used C4 control parts out there but there is no way to check and see if it works untill you plug it in and see what happens.
The controls can be updated, Milltronics sells a C7 control update for about $8K plus install.
drives, motors etc can be replaced with "current" products.
the iron was good but is no longer made and replacmet head parts are not available, ball screws if needed may have to besent out and remanufactured.
sorry to say, it may be better if the machine were parted out, or you may end up being the one "looking for parts in all the wrong places"
as for the 4th axis thing, a seperate 4th axis control board mounted to the main control board along with the a axis drive board was needed to have a 4th axis. again these boards are only available in the used market
imo you would do better looking for a newer machine with at least a C5 "-B" version control. in contrast a new Milltronics knee mill, VK-4 costs about $35K
If ended up buying this P3 PM me for more info
Not too late at all. I appreciate all the input. The seller stated he was going to be busy through the end of June, and I haven't heard from him since that call (early June). I don't mind spending more money for something that is going to be a "better" unit.