Ok some of you asked for an update. I decided to just put a 51 jet in. I am now getting 17 mpg.
It has less power than with the bigger jet but still runs good. I may try the 53 and see how it does.

Well, this may be too late to help, but I finally took apart the 1920 off my '68 V200, it had a #55 in it.
It was stamped on the side like every one of the 40 or so Holley jets that I have, not the end or face.