OK Jim
You will have to clamp the central bush, you need some round bar faced on both ends to support the bushing from underneath, now you need a strongback to clamp the bush from the top, you want a piece of substantial flatbar with a hole larger than the size you want to open the bush out to in the middle with a couple of holes clear of the mounting main body and so you can allign with the slots in your drill table so you can secure the strongback to you drill table with studiron(allthread) make a dolly to go in your chuck with one dia original bush size and second dia size of clearance hole in strongback, then allign the strongback with the bush bore and tighten the job down using the studiron.
Sorry it took so long to reply had a visitor.
Mike