Help I.D. this brake booster and recommend dual master cylinder please

[CPO1]

This topic is discussed alot and I've read most of them. I come away with some confusion still so here's my specific situation.

This booster on my 65 GMC and the PO added it in 1990 or so. Has drum/drum. The engine is a small block V8 that's got a bit of a cam. I find the truck starts out braking like it is powerless then as i apply pressure it begins to brake better. Regardless that single master has to go and i have to run some vacuum testing yet. At this point, I think the booster is working properly but I am unsure how much vacuum I'm working with.

My questions

Is there a better booster for a cammed engine?

What dual master would fit this one I have now?

Or If I should replace it, with what?

Thanks.