Hi neighbor, I would not buy a round ram because like you said it can’t nod. The newer dovetail versions can move in both directions…Dave.
Round ram mills (I have a 1948 "M" head machine), can nod, tilt, and swing. In the picture above it is setup to tilt and swing. You have to turn the ram 90* to allow it to nod. In the picture, you can swing the head to the side then tilt the head, allowing it to artificially nod.
There are two ways to tilt the head on a round ram, using the worm gear on the turret casting or the front 4 face bolts that actually hold the head on.
If you have one of the round ram to "J" head conversions, offered from around 1951-53, (before and during early dovetail bases) you don't have a knuckle. In that case you can only tilt the head.
Round ram machines don't have a worm gear to nod them. If you loosen the knuckle bolt there is a safety pin to hold it in place, but if you remove that the head will fall. Make sure there is some boarding under the head to keep it from falling. (Stack wood between the table and head, lift knee to apply some upwards pressure, remove safety bolt, loosen knuckle clamp bolt, lower knee to tilt head. At some point the head will slip off the table and crash, be very careful when nodding)
