You're going to need a female Merc connector. The only question is whether you need the small or the large connector. In the 60's, mecury introduced a small version of their normal connector. They only used it on some of the 3.9, 6, and 9.8 hp outboards. They discontinued the small connector after a few years and that has caused the small connectors to sell for a premium price today. You can find the normal connector for $10-$15
https://www.iboats.com/5-16-Barb-Fuel-Connector-Aluminum-Sierra/dm/cart_id.099290512--session_id.310146622--view_id.187424
while the small connector will set you back about $50 https://store.oldmercs.com/product_p/30635t3.htm
I believe they only used the small connector on the 6hp from the early 60's, so you should have the large connector if your motor is a late 60's.