Yea, the phasing harness lengths are critical. It has to do with getting the timing right with a carefully trimmed length of a cable with a known (preferably measured) velocity factor. Knowing it's RG-11 helps.

That being said, a single 50 Ohm connector in a 75 Ohm harness would probably not change too much. You could modify the harness slightly to accommodate the small change... and you'd have to measure it.

Much simpler to get the 75 Ohm connector. But I wonder how much it would change?

Every harness I have made I used extra coax and connectors, cut and measured a few till I got it just right, and then made 'em. So far, just two meters, and the MFJ analyzer showed me what was going on really well.

Modified the 2m loop design from this page, for a pair of 2m loops...

http://www.kr1st.com/2mhalo.htm