Mantua used common parts wherever possible. For the 4-6-0, what engines shared the driver size?
I would guess they would likely be the same drivers as the large 2-8-2 or camelback 2-8-2. The 4-8-0 used the same boiler as the 4-6-0 but had the smaller drivers used on the switchers 0-4-0/0-6-0.
I think, someone correct me if I’m wrong.
^
That is my guess too. I have an old wreck of a Mantua Mikado with a torn up gear on the driver and was looking for a cheapish replacement. The Mike isn’t planned for real use since I’m now playing with N scale and modern models. Still, it would be fun to get it running with some small upgrades. (An old monogram hudson kit can provide some parts. 
)
If you go to this site, you can see the instructions that came with any of the locos and compare part numbers: http://hoseeker.org/mantuainstructions.html
I have a old Mantua that measure 0.465". 50 inch drivers. The drivers are close together.
An old Tyco that measure 0.695". 60 inch drivers. The rear drivers spaced away from the two front sets.
Rich
Looks like the gear is a different size, the rest is the same.