using piston stop

The commercial ones are not very well thought out. You need a jam nut on the rear of them to lock the plunger. As above it must be rigid this is the one I made for a SB in the 70's and (miracle) LOL still have it

stop2-jpg.jpg

It's not very important how long it is except that you don't want it too close to TDC. You want the piston to stop "down a ways"