Other than some careful layout and some careful hole drilling, the twin screw hasn't been that difficult to install. Did need to use the Forstner bit extender to drill the holes through both jaws at the same time in order to insure they aligned properly.
Speaking of careful hole drilling - when was the last time you checked your drill press table to drill bit alignment? Been a while right? And that table's been cranked up and down, pushed down on, pullled up on and maybe you've changed chucks once or twice since you last checked the set up? And if your drill press is on wheels, you use he table as a handle to move it around? Mine was out of square in both the left/right and front/back directions - by probably 5 degrees. For a hole 5 inches deep that can be quite significant. Word to the wise ...
Because the bench top core is two 1 3/4 inch thick laminate maple slabs the top of the vise screws are set above the bottom of the top and ALMOST above the bottom of the bottom slab. That probably doesn't make any sense at all so here's some pictures that should clear things up a little.
The instructions suggest putting "rub blocks" under the screws to support them when the vise jaws are at maximum opening. Had to route 3/4" grooves in the bottom of the bottom slab, cut rosewood blocks and route half round grooves in the "rub blocks". Put them in with a single counter sunk screw in each - might as well make it easy for them to be replaced - by me or the next person to own this bench.