EDIT: I SEE you have HIF carbs. Not HS. Those should last longer (throttle shaft bushing wise) than HS carbs.
Here's a few notes from a slight newbie when it comes to b20... I learned the hard way
Your going to need to buy a fuel pressure regulator for that weber. A high quality one at that. No kragens junk
#2 a big jet kit to get it right. mine was jetted huge compared to stock and still pinged without retarding the timing
#3 you will also need to run a intake coolant line for the winter (I disconnected mine in the summer)
You will get a constant sucking sound from the single barrel wanting more fuel and air.
Intake manifold was designed for a b18 not b20
You can get your carbs done for cheaper than 600... I found a guy who does rebuilding and new bushings, shafts for under $300. Redwood chair Gabe me his info. He even made a blog site showing his setup and him working on a carb. He said he pays way less than what we can for the real SU carb kits so for the price it's a good deal.
I pulled a set of SUs off a junkyard car and have been running them for over a week now no problems.
The progressive is a pain to tune because you have to take it apart for jetting. I love how simple the SUs are.
If anything I'd say sell the brand new progressive and buy a synchronized non progressive 38mm weber.
I have heard opinions that its an improvement and that they are terrible. I think it mostly has to do with how well you can get the weber tuned vs what sort of shape the SUs you removed were in. The SUs are original so like 250k miles. They need a full rebuild and the price for this weber kit was less.
Plus I like how the single carb simplifies the look of the engine bay. If it really is that bad to drive with, I will start rebuilding the SUs and swap them back.