There is not much you can do to stiffen up one of those lathes besides adding mass. Not enough cast iron in the bed. Bolting to the floor might help but completely depends on the cabinet it is sitting on. I would suggest building the heaviest, stiffest cabinet you can. A 3" thick poured concrete top would go a long way toward damping vibration from that lathe. I have a 6x18 and a 12x36 and found that adding ballast to the table and underneath helped significantly with surface finish.
I have seen lathe bases made from cinder blocks with a slab top and you wouldn't have to worry about bolting that to your floor.
