Hi Derek,
Another 'Welcome' to the forum. Always good to see a new turner discovering the craft.
I seem to recall Record toolrests were supplied in two post lengths. One was to fit the older banjo, which was locked in place with a handle underneath, where the hole for the rest went all the way through the casting. The shorter one was necessary for use on the newer 'camlock' banjo, where it is locked with a lever on the front of the banjo, but the cam rod was under the hole for the toolrest, thereby limiting the height adjustment.
We've got a club meeting tomorrow and I should be able to get a definitive answer on this, so will post again on Thursday. But, as has already been said the easiest option could be to cut a bit off the bottom of your existing toolrest. However, if you do, only take a bit off then try it out. Like wood, it's easier to take it off than put it back.
Aside from that, hope you are enjoying your turning,