Have you tried running them yet? Look through the side of the Pacific over the middle driver and see if you can see whether there is a gearbox or a worm gear directly contacting the main gear. Either type will work fine, although you may need to do a little cleaning and oiling. If it has the gearbox which the older Mantua's sometimes had, and which the much newer one also did, it is very easy to convert from the open-frame motors to a can motor, and convert to DCC for sound and smoother running, although the direct-drive/open-frame motor jobs are pretty good as-is. The Pacific will handle 18" radius curves easily. Sorry, I don't know much about the Kemtron. I'm probably wrong, but the chassis looks suspiciously like a Mantua Mikado one, although the boiler and cab are probably not, unless it is one of the very early ones. Someone obviously had detailed it with various piping, linkage rods to the frontend throttle, etc. Can't tell from the photo how the tender and the engine connect. Possibly with a pin connector, as opposed to an insulated drawbar and separate wire to the tender for electrical pickup, which is what the Mantua Pacific uses.
Let us know if you have any questions.