I am having a hard time installing the fuel lines to the carburetors on a 340 six pack engine. Should the fuel lines be installed as a complete unit or should they go on as individual pieces? Any tips would be appreciated. Thanks.

just put mine on and did it in one piece. very easy.put it together loosely and get into place then tighten down. good luck

OK,
I will give it another try with the complete fuel line together. Thanks

Should I apply some sealant on the threaded fittings?

no. the lines are flared. the inside cup of the flare fits into the concave parts of the mating fitting. the thread do nothing for sealing.