I had one of those too. My list of mods is long and plenty.
Replaced the drawer slides with 100lb slides that also happened to work. This is a cost prohibitive mod but I got the slides all for free.
Next was X bracing on 3 of the 4 sides. I used angle iron that I cut out to fit.
Throw the vises away and find a used Columbian, Wilton, etc woodworking vise to rig on instead and then a machinist style vise mounted wherever you desire.
Never liked that bench and left it at the house with the new owner.
Looking back on it I would have done things tons differently. I would have thrown away the top and made a new one 3-4 inches thick. I would have tossed the legs and made new ones 4-6 inches thick. Then I would have chucked the old stringers and made ones 3x6 inches mortised into the legs and drawbored. The drawers.....they were handy....throw them away too and mount some kind of toolbox under there. Top chest, lista....something.
The drawers are really the only thing that makes that bench tempting. As far as the bench structure, it is ****. You could do better with a 4x8 sheet of 3/4 ply ripped in half and doubled up for a top. Then use 4x4s and 2x6s for the legs and frame. Heck, pocket screwing it together would probably even be OK. But the drawers are going to cost you something and that is where this HF bench gets you somewhere.