Holley 1920 diaphram return spring

Yes, if you want the twin-carb setup to run well, the carbs need to be matched -- not just the same jet number, but identically matched carbs in equal and excellent condition. A pair of new and matched 1945s are going to be a lot easier to find, and do a lot better for you, than trying in probable vain to cobble up two worn out 1920s or BBSs.