The Alu will weigh about 18Kg, the rails probably a wee bit more each.
The frame however is fairly sturdy being made out of 3 and 4 inch steel box with 1/4 wall, so plenty of mass there and if need be I have a steel cabin housing it that it can be fixed to
It will be servo driven via a 10:1 gearbox so max cont torque available would be in the region of 20Nm and peak 70Nm peak.
I have some heavy wall tube that may do the job but if not a solid shaft will probably be employed although I prefer to keep the weight down if possible, will have to do some calcs and see but I do know the original machine that the racks etc came off had a 30mm dia solid shaft of about 4m.
It will just be spinning at a few hundred RPM max .
Using two motors would add more weight to the gantry than a solid 30mm dia shaft would be anyway.
Hood