Mixing and matching is futile unless you're pulling them off engines. Small-block and big-block have the same water-pump bolt pattern and crank damper pattern (though B/RB changed one bolt hole, I believe in '73, but that's an easy fix with a rat-tail file), but there are several variations and offsets of both kinds of pulleys.
Don't even mess around with pulleys until you have brackets with all the accessories mocked to the engine, and can see how far off you are with what you've got now. My advice would be to call Douchillon and ask them what pulleys you should be using with those brackets. They will almost certainly get you the right parts.
The worst pulley nightmare I ever endured was my Trans Am. There are three variations of brackets and pulleys for the 400; one of them is a half-year-only deal (1969?). I had parts from all three, lucky me. There were a disgusting amount of shims and flatwashers in that arrangement to keep things aligned, but it made the alternator mount a bit flimsy and I still had belt noise/loss problems. I eventually got it mounted more solidly, but the washers and shims remained.
It comes down to how much your time and aggravation are worth. :huh: