Assuming that some used but good (or rebuildable) tappets are available, rather than the "correct" .990" units, the obvious cheap install is to combine bushing down the tappet bores to the roller body OD, and slotting the bushing ID for a locating pin.
A GM .842" tappet leaves .074" of wall thickness. Also saves a few grams.
There may be GM tappets short enough that the original link button would be inside the tappet bore, which allows simply milling the button down to fit a bushing slot, like 1/16" deep by 3/16" wide. What's bad about this is that it uses only a single point of alignment taking all the load, and it's on the thrust axis where bushing wear is highest.
