Steve-- To the very best of my knowledge, the 519 was only a 10 gallon pump. What you have there, is an example of someones craftsmanship in shortening the markers after their cylinder got shortened! The positive stop mechanism on those pumps is so complicated that there would be no reason to make a 5 gallon version! Besides, they were designed to set the stops for 5 gallons, and that was what the pump delivered, so why would they ever want a 5 gallon version or any other version for that matter? They thought they had it licked!! One pump with 10 different settings!
Worst part was the amount of moving parts that tended to fail, and were removed I order to make it usable as a regular 10 gallon visible!