I think the MTH cars represent a much later prototype open platform car from the 1880s or 1890s. The Lionel cars from the picture appear to represent more of an 1850s-1860s civil war era prototype.
As for running them together, probably the prototype did not. The 1860s cars would probably be retired except on some shortline are rare branch by the time the 1890s cars were in heavy use.
The lionel cars would be very appropriate for the civil war era 4-4-0s such as the general represents. the MTH cars would be too new for that and would be more appropriate for a much newer 4-4-0 such as the one MTH did or a 4-6-0.
