1/15/2020 Update: Had a great experience talking to Ron over the phone at the Daytona Carburetors company. Sounds like a nice small outfit. Very knowledgeable gentleman. He took his time to listen to my technical questions and answered them clearly and calmly. It sounds like he's been working with carbs and in the automotive industry for a long time. What I learned. One is that originally GM ran the Zenith carburetors on these engines, (im not sure if he was referring to the 261's or stovebolt engines in general) and that these are a direct copy of those zeniths. These had the 32mm venturi on them, which was meant for these engines. I was happy to hear that and that they were OEM equipment on these Chevy's, that makes us purist a bit happier. I mentioned that I wasn't getting the high end performance I was getting before with my Rochester, he mentioned that perhaps my air cleaner wasn't allowing enough air to enter, or I simply hadn't richened the high speed jet enough and that I should first find out how many turns I had in fact turned out, by starting from the start (turning in and bottoming out the needle, its a very fine adjustment as I was told). I found out I was 6 3/4 turns out. I went 1/2 turn out more as instructed to see if that helps and to keep going out in half turn increments to see if I notice an improvement. He also suggested I test-run my truck without the air cleaner to see if that improves it. Another thing I learned is that the carb kit comes with a plastic red adapter to accommodate for larger air-cleaner base plate openings. He mentioned the diameter I believe it was 3 1/2 in. for the earlier type but they changed in 1960 I believe he said. I didn't quite understand how its supposed to work. Another thing I learned: I mentioned that I was looking for an adapter fitting (male to male) that would go from my glass bowl fuel filter to my UN2 carb. The one I had that worked on my Rochester was 1/8th to 1/8th mpt. but the inlet for the UN2 is a metric thread. So at no extra cost, (since I had ordered the carb from them) he said they would send me the 1/8th to metric fitting to my address so I can run my glass fuel filter again. Great customer service in my book. He wants me to follow up after I try the adjustments. Very content with my experience and am looking forward to dealing with them again in the future. p.s he also suggested I run only 87 octane fuel because it has a higher boiling or percolating point which is 180-185 degrees Fahrenheit while 93 octane is approximately 40 degrees lower around 145 degrees Fahrenheit. Good to know.
