You need the vacuum set up as with the Carter. If the Rochester is set up to send manifold vacuum off to the vacuum advance unit on your distributor, it is good you're replacing it. I don't recall seeing any of the Rochester "B" types that weren't designed for ported vacuum, but I could be mistaken. The 235 distributor uses centrifugal weights to provide any needed advance at idle (and at 500 rpm, it won't be much) and the vacuum canister will kick in around 850~900 rpm when you reach off-idle status. The manifold vacuum at idle ought to be around 16~18 and if it is, the vacuum canister will provide much more advance than you need. Hope this helps. Please don't hook your vacuum canister to manifold vacuum.
