I have been practicing some CAD drawing. This is the basic structure of the gantry showing the V-plate bolted to the aluminium extrusion. I will likely have the plate and the drilled and tapped flat bar to bolt it into the Ali extrusion laser cut and countersunk and then use the Mechmate grinding skate to grind on the V-track or have this section machined.
Notice that the gantry extends a fair bit over the bed...this is intentional for mounting a potential future 4th axis or to machine assemblies that don't fit onto the bed.
If I find the construction to lack stiffness I will likely reinforce the Ali extrusion with some steel angle bolted top (or even bottom) to the 45mm sides of the extrusion and perhaps attach the R&P drive to this angle iron.
I hope to receive my Z-slide back from the machinist sometime this week which means that it'll be time to work on stepper mounts soon.