Arty,
you have two different engines there, the one with the aluminium flywheel looks like the engine with the 45mm bore and the other may be the 50mm bore. You can also see the different construction of the mowers, the what I will call the English mower has angle iron as a frame between the sides, I have not seen this before not that I have seen all Atcos, the other has the rod with pipe spacers holding the sides together, this is the common construction that I have observed, the clutch is different on each mower, the English has a 3 piece roller whereas the other is a 2 piece roller.
I am hoping that someone with more Atco knowledge than me can help us both here, looking at the numbers I would say that one is the 8th month 1948 and the other is the 7th month 1948, but this begs the question why the differences in the mowers?
It may be a silly question but have you actually measured the cutting width at 20 inches? There was a 17 inch model that had a 2 piece rear roller and the 20 inch cut had the 3 piece roller.
I think that I have confused the issue more than helping, but I am sure we as a collective will get to the bottom of it.
Beech.
