Hi, Oldrnu.
That looks more like a 22.
Just my 0.02.
it is a 20
I agree with Jeff it's a 20
i am shore its a 28,
(the re-designed 20 and 25 as base machine but with some new modifications) as the back of the seat has the chopped of corners, and the radiator sideplates have Caterpillar on it, ( radiator plates of the 20 and 25 had twenty and twenty five on them)
I vote for the 28.
the final drive hubs are small it could be a early 25 but not a 28 with the hubs so small
Looks like 28 to me....