When doing a little research on Orgeat, I found many Mai Tai recipes. This one, as near as I can tell, is about as close to the original 1940's Trader Vic's recipe as we're going to get. That recipe called for a very specific 17 year old rum (Wray & Nephew 17) that has pretty much been drunk into extinction.
I've replaced that same amount of rum here with a 3:2 part mix of non-specific aged rum and light rum. I'm not trying to downplay how great a bottle of Wray & Nephew 17 is — but let's face it, if you happen across a bottle of $50k rum, you're probably not going to taste it in a Mai Tai. Just sayin'.