What a hoax - & I know Zeniths...the ZS carb isn't the problem with that factory setup - its the manifold...& anybody who falls for that 'performance' bunk deserves to lose his $479! Plainly put: there's always something to take a sucker's $$$'s!
What's easier to tune about the single SUversus the ZS? Both have the exact same adjustments, just getting to the needle is a little different.
...& manual choke? HA! I've got almost 100,000 miles on a ZS carb that's been rebuilt once since it left the factory - & it still has its water 'choke'....no problems!
....will you get more power from the single SU? Not so long as you put it on the ZS intake manifold with its required catalytic converter - heck even without the cat you'll not notice $479 worth of power increase so long as you're sticking with the original ZS manifold....if I wanted more power from my '79 Vermillion Red B, I'd switch to dual HIF-4's (oh, wait, I did on my '79 Pageant Blue B!)
...but, to each his own!