G'day Matt,
The short answer is no, the two carbs don't need to be exactly matched. It's nice to have the same number on the side of both carbs, but a clever bloke realises that most of the grey carbs components are identical.
The link below is to my Stromberg Guide - take a look at page 24 for the different grey motor carb specs:
FB/EK Holden Stromberg Carburetion Enthusiasts Guide The carbs you are looking for are 23-105's, 23-3000 and 23-3001. The really significant differences are the power bypass jet (which you will probably change), and the main discharge jet (which you will probably not change). In short, you want a grey motor carb with the same main discharge jet as what you have (28-34).
This means you should be hunting for another 23-105 carb (23-105A, 23-105B, 23-105C or 23-105D). You then change main metering jets and power bypass jets to make them both the same, and to make them both smaller for the twin setup. I can help out with both the main metering jets and power bypass jets when you get to that stage.
I've probably got a spare 23-105 in my spare parts stash. I'm on the road for work at the moment though - give me a yell in about three weeks if you are still looking.
Cheers,
Harv
