Single Weber Progressive carbs used to be the big thing w/ACVW engines (4 cyl air cooled boxer engines) but have fell out of favor due to their tuneability issues, i.e. always needing adjustment and hardley ever getting setup right.
The "best" carb solution for them (1600cc & up) is to go w/dual carbs. Depending upon the size and performance desired, dual Webber 40, 44 or 48 IDF's (excellent for street), Dual Webber 44 or 48 IDA's (excellent for strip) & dual 36 or 40 Dellorto's (excellent for street) are preferred. Each of these carbs are 2bbl so basically each cylinder has it's own tuneable bbl.
Other options are dual 1-bbl's which include dual Webber ICT's or Dual Kadrons.
There are many vendors to purchase these carbs new and/or rebuilt and if I were to go the dual or triple route w/any of the above I'd choose the dual Webber IDF's. They all can be rejetted and even have the venturies resized to fit an engine.
I know what I'd put on my 72 ACVW (Karmann Ghia)& how to rejet it but at this point I have no experience w/adapting any of these to a stovebolt. Course who knows on down the line

To the OP. as been posted, the carb kit you refer to comes in dual carb pkg's and if you go that route you'll also need to change your intake manifold to an aftermarket type that accepts 2 carbs. So there will be more involved than just a carb change.
The info I posted above is more rambling than being helpful to your question so disregard it and listen to those who have BTDT

Good luck
Dave