Don't think I've seen anyone mention the 6.5x55 as ever being made in a handi, I believe it was listed on our wish list. I know the 7x64 was made at one time, though. NEF and H&R are one in the same, both owned by Marlin, now. The Handi is an NEF, the Ultras are branded as H&R, but they all are sold by H&R, if that helps any! Kinda confusing, I know. A handi or an ultra comes in a box marked with NEF on one end and H&R on the other, FWIW!! As far as barrel fitting anNEF or an H&R, yes if it's ofrecent origin, some of the older H&Rs may not fit well or at all.
hope this helps,
Tim