Although to late for Dusty to use I had a Greenie I restored and the base had a broken out hole. Actually the end one that I repaired with aluminum rod brazed in to fill the space than ground down to match the original profile. Could also be done as Everett suggested by someone with a MIG or TIG welder that is set up for aluminum welding.
I would suggest that you put the new holes as close to but not to close to the original holes as possible to maintain the strength of the original design. On the end maybe a new hole on either side of the original would be good. New hole locations as shown by the red arrows in the diagram below
Remember using this as a workbench frame it was designed to carry a certain amount of weight but not designed for repeated impacts/hammering.
Mark V 520 S/N 09-11-01 completely upgraded to Mark 7, with all SPT's & more.
Model 10ER S/N R64000 first one I restored on bench w/ Shopsmith metal ends & retractable casters. Has Speed Changer, Model 4E Jointer, Jig Saw with lamp, a complete set of original accessories & much more.
Model 10E S/N 1077 oldest one I have restored. On bench w/ Shopsmith metal ends & retractable casters.