All the parts are interchangable. MK1 and MK11 Boxfords are 4.5" and the MK111 is 5". It doesn't matter if it is an A, B, or C model. The gearbox is pretty much the same from the earliest rear drive models up to the last of the underdrive models and will be interchangable, regardless of centre height or age.

The 5" models have a slightly taller headstock, thicker base to the tail stock and a slightly meatier compound to make up the extra height. Other than that, no real differences.

The B and C models even have holes drilled in the bed to mount the gearbox without modification.

To upgrade a C to an A you would need the gearbox, leadscrew (you may be able to modify the original leadscrew) and apron. I think the saddle is the same but I'm not sure as the C didn't have power cross feed. It might just need an the cross slide leadscrew swapped over.

Edited By Gavlar on 21/08/2021 23:38:06

I upgraded my 5" ME10 from "B" to "A" spec. by fitting a gearbox from an older 4.5" lathe. No problems, the main job was shortening the leadscrew to connect to the gearbox output shaft. As it will pass through the spindle, machining was straightforward.

I assume that the "C" lathes have the necessary drive keyway in the leadscrew even though the longitudinal feed uses the half nuts.