The vise slipping at the start of a hole has been frustrating. I found that the collars did not pull the screw shaft tight against the plate. Even after tightening the collar the hole in the plates had enough slop to allow sliding during a drill.
Removing the handles, collars and plates is easy enough. This allowed me to make some measurements of the parts. The screw shafts are 12mm. I found KFL001 flange bearings on eBay - 2 for $7.70 delivered. The Longitudinal Slide needs a carrier plate and the Transversal Slide needs to have the flange housing milled about a 1/84" on each side for socket cap screws to fit in the original holes. Following are layouts for each.
So far the results look promising. No more wiggle waggle as the slides move from end to end. My intention by using a bearing was to eliminate the slop in the plate hole and by using the inner race set screws and the collars there would be less backlash. However the bearing also made adjustments smoother. I am not sure how well the zinc flanges will hold up. Maybe there is a simular bearing with a cast iron flange.
Milling - there are as many opinions about using a cross slide vise and drill press as people who have this set up. Here is mine. With practice and patients small tasks can be completed with reasonable results. I have worked ABS plastic project boxes, softer grades of aluminum, and even A36 steel.. A ER20 tool holder with a Morse Taper 2 works much better than a drill chuck. I have a set of 2 and 4 flute end mills all with 3/8 in shanks. The wider the cut requires more passes to get depth. On a A36 flat bar I cut a 0.050" grove with a 1/4" end mill in 6 passes. It is sort of OK, there are visible chatter marks on the side walls. For a garden tool fix it will work, for standard shop work, not so much.
Disclaimer – Determining suitability of the modifications described here or skill levels needed to make these modifications is solely the responsibility of anyone choosing to replicate the modifications. There is no intent to criticize the Harbor Freight products described here. Please be advised, the suggested modifications have not under gone any safety review or risk assessment. Proceed at your own risk. These modifications are not approved by Harbor Freight. Moreover, Changes to the Harbor Freight items would probably void any warranty by Harbor Freight.