Did some quick measurements the other day. The Hammond vulcanized rubber shuttles are .2 grams lighter than the metal Varityper shuttles. There’s also a slight height difference, with some modest trimming on the metal spine. Collectively these changes make it difficult to use a Varityper shuttle in a Hammond.
But there is hope…
In order to get a Varityper shuttle to work on the Hammond, the shuttle arm needs enough power to move the shuttle to the correct character. One way this has been done is by replacing the hammer; I don’t recommend this. The other way is to put in a more powerful spring on the horizontal drive arm.
The spring has a loop on one end, and a hook on the other, which you may need to create yourself by snipping one of the hoops. This is a good replacement spring: Steel Extension Spring with Loop Ends, 0.625″ Long, 0.188″ OD, 0.016″ Wire Diameter. McMaster-Carr
Spring to increase the tension so you can use the Varityper shuttles: Music Wire Steel Extension Spring with Loop Ends, 0.625″ Long, 0.12″ OD, 0.022″ Wire Diameter
However, note that this may still not be all. Depending on how old the machine is, you may need a bit of lubricant. Ultimately it may not work but it’s a good try. Both links should take you to McMaster-Carr’s website where you can find every spring imaginable.
Update: After a bit of testing it IS possible to use a Varityper shuttle on a Hammond Multiplex. You’ll just have change the springs, but know it may still not work. Slight variations in manufacturing and the built up of dirt etc. can slow things down.