Rosscoe,
The HEI setups are self contained, coil is built into the cap. Some may argue this, and experience varies, but they are advertised to have alot more spark throughout the rpm range, and don't fall off at higher rpms, in any application that applies to us anyway. This has been my experience every time in straight swaps changing nothing but distributor. Always a very noticeable difference just in all around running. You may have to adjust idle and idle mixture to adjust for the better burn. Again, I can't guarantee this is your fix, but man does it sound familiar! You could put a clear fuel filter at the carb, run it till your issue arises, immediately shut it down and check the filter. If there's fuel, can't imagine how it would be a fuel issue. And no, it's not a marine setup, but you could seal the vent better or tap in a vent hose to route elsewhere, but all the performance boat sites literally have hundreds of guys running street setups without issue. Doran I believe is running something very similar with great success.