Bolster, front axle and steering are 3000. Transmission and rear axle are 4000. It has its own engine.
3055 is not properly presented in the parts lists. 3550 is the industrial version of 3055, and that is presented together with 4000 in the hydraulic lift section. 3055 should have been there as well. I do not know if they made changes during the years, with different lift piston/cylinders. However, according to the dimension that Mrdoc gave, it is a 4000 piston.
I cannot find any reliable information regarding the dimensions for different part numbers. Some vendors say that it is the same piston for 3000 and 4000. This site tells that the 3" piston was used on the early (Pre-Force, 6X) 4000 and the larger one on the later (6Y). There is no information about that in shop manuals, so I do not know:
Ford & Fordson100 Series:2600, 36001000 Series:2000, 3000Fordson:Dexta, Super DextaFord 4000 Pre 1968.Diameter: Ø 3" (76.2 mm)Replaces: C5NN530B
histoparts.com
Piston diameter 84 mmOEM: C5NN530A
histoparts.com
To be safe, ask the seller to measure the diameter of the piston(s) they offer.