Sub-table for a Bridgeport mill...

I'm almost ready to move my smaller parts to my Bridgeport conversion from the mini-mill. The spindle mount adaptor is made and the wiring/programming should be good to go. The bed needs to be about 350mm x 450mm

This is my mini-mill with a just-finished part still mounted, I need to make a sub-table to replicate the bed of the mini-mill on the Bridgeport.

Attachment 19173

So, what would i be looking at here? The existing bed is 15mm ecocast but is sitting on a 15mm slab of cast iron which is bigger than the sub-table. The Bridgeport has a relatively narrow table at 230mm so the sub-table will overhang, max rear overhang is 20mm so more to the front. This lump of MDF is about the right size, sitting on the mill...

Attachment 19172

Now, I have about 5 parts i make occasionally, none in quantities big enough to deserve a custom fixture plate so the universal sub-table seems the best way forwards?

What sort of thickness here?
Would it need support arms underneath for the overhang?
How to mount easily onto the Bridgeport?

Better idea?

Gone for a slab of 25mm tooling plate, fitted two dowels on the rear to locate in the bed slots, milled in some alignment features for picking up datums if needed, just got the matrix of holes to drill / tap - will get to try my tapping head out :)