He took apart the hydro lifters and effectively made a fixed pushrod seat with an oil hole. They would work with your 89 roller block (same spider and retainers as the non-magnum roller).
The modified lifters don't seem to be available anymore, and other forums/posts allude to issues/failures of these lifters that others have experienced.
If an aggressive cam is used in a roller block with OEM lifters it's probably just as effective to lash them solid and then back off 1/8-1/4 turn. Pump-up shouldn't be a huge concern if the car has a rev limiter and good springs.