A couple thoughts on spacers, not all-inclusive by any means-
Often as not, a spacer is a trial and error type thing. The best thing I can suggest is to do runs both with and w/o to determine whether your combo 'likes' one or not.
There are rules of thumb that I've heard through the years- "only use open spacers on open intakes"; "4-hole spacers only help the bottom end", "open plenum spacers need to be 2" to matter", "if you use an open spacer on a dual plane, it'll kill the bottom end", etc, ad nauseum. For every one of these "truisms", there's instances of the opposite results being obtained.
Sometimes the positive results are nothing more than the insulation properties of some spacer material that isolates the carb from heat.
A spacer WILL allow the fuel/air mixture to make the turn easier into the runners, this extra distance and increase in plenum volume can result in less signal felt at the boosters, which in turn can require more jet to compensate. Or not- that's the reason that you have to try them and compare the results.
Best bet IMO is to try them all and chart the results unless you have access to a dyno.