My understanding of this problem of 4 different front mounting plates is as follows. (I am sure someone will chime in if I am wrong!). The change at Engine No 1599502 was the fitting of a new type camshaft with a single bolt fixing for the camshaft gears, rather than a 3 bolt fixing. At the same time, the camshaft end float control "system" was changed from a horseshoe shaped thrust washer to thrust being taken directly onto a machined (and hardened?) face on the front mounting plate. You should have a single bolt fixing camshaft, requiring no thrust washer, which requires the front mounting plate with the appropriate machined camshaft aperture.
I also found when trying to assemble my NP Super Major a few years ago, that the heap of engine bits that were handed over (the tractor had been "Stripped for restoration" by the previous owner) included timing gears of 3 different widths, but not a complete set of one type!
You can see the oil pressure valve in this picture.
Other differences in the plates, the "B" type did not have locating dowels for the front plate, should not make any difference as you may never come across one unless its on a very early Major. The "B" type is the one wiith the reliaf valve.
The New Performance front plate has bigger stud holes as the retaining studs were increased in size.
Fordson Tractor Pages, now officially linked to: Fordson Tractor Club of Australia, Ford and Fordson Association and Blue Force.
Brian
Does anyone know if the holes for the generator (two of number one in the pic) are moved a bit for example between mark2 and mark3 engines? A friend told he suprisingly got misalignment between the holes in the engine (old block) and frontplate when changing generator and brackets.
1958 Major
1953-59 mix with backhoe Hymas type 3 (project)
1961Selene 4wd (project)