Seems to me you have the opportunity here to have a proper gap bed lathe?
cheers but theres two problems I can see with that; the first is strength, gap beds have a lot of material around the gap to make up for it and I think just adding to the sides at low level wont help much.

The other problem is the apron is large and actually goes past the front edge of the headstock for normal turning. so the dropin piece would be permenatly in.

If i remake the bed then I will definetly make it a gap bed as i can design in the additional strength.

In hind sight I should have just bolted strengthing plates to the side as you suggested and filled the holes with chemical metal.