I think there are 7-blade to 7-round adapters, but the point is that may not be enough in your case. I know my '75 Argosy's original pinout did not match the modern, essentially standard 7-pin pinout. It may be that someone has already fixed yours and you'd just need the blade-to-round adapter, but unless you're planning to change your Excursion to a round-pin plug, you might as well update your umbilical end to match the Excursion so you don't always need that adapter and so you don't have 7 more connections that might get dirty or otherwise fail.
Il Carriaggio — 1975 Argosy 24 | Il Progetto — 1976 Argosy 28 Center Bath | WBCCI# 15566
He has all of the virtues I dislike and none of the vices I admire. — Sir Winston Churchill