Timing with either the left or right timing marks won't lead to a breakage of the pump. The only way to screw up something by timing alone on one of these is to change the timing on the gears, which would lead to bent valves. (Wrong marks used = won't start)
Are the pumps you got new or re-conned? Most re-conned parts usually don't have a lot of markings of any type. Have a disassembled pump needing to be rebuild, if it is fine with you I can post pick in a couple weeks time.
Best pump set tool, better than a piece of saw blade, is to cut the tail of a cheap vernier or use one of these plastic card, material, salesman verniers and altering the mouth to look like the beak of a bird that flew into a windscreen. Small inside leg calipers also work when you have adequate access.
You broke the pump by setting the stroke of the follower so far that it crushed the piston of the pump, ie stroke of pump was exceeded by stroke region of follower, and the only thing that could give was the pump body.
I had engines in the past, other models, where the spill was set to far either bending the cam/ breaking cam bush housings/ breaking gears on the timing train, not on PH models though, so you are extremely lucky.
Slackening the pump won't tell you anything as the pump is spring laden and will rise. After setting spill the pump is left alone and the engine while decompressed is turned slowly by hand, preferably without a crank to attain if the bump stop is exceeded.
On Rustons, small one's, the follower is of the plunger type with set screw that bends with excessive force, pump bodies can be cast iron.