This question seems to pop up regularly. I had to pull out my yet-to-be-installed kit for another reason so I thought would take a couple pics.

The Redline (no affiliation) smog-legal Weber kit, K8747, comes with a one-piece adapter. I don't understand why they don't use this adapter for all their 20R kits. I think you can buy it separately.

Hope this info is of use.

 

If you can't find the Redline one-piece adapter, Transdapt (no affiliation) sells a one-piece raised adapter.

 

Most of the Weber 32/36 sold on the secondary market are “Grey Market” carbs. They’re Weber clones. Redline is the official Weber Carb.

Grey market carbs can be had for about $250 vs $350-400 for the redline. The two piece adapters were just poor engineering. Other than that there really is no difference in performance.

 

The one piece can help against heat soak and more importantly sealing. Anyone woundering. To add to the picking out a carb they do come setup from redline. So you want to make sure you get one that is for your motor. So if you're looking to buy local and already buying the one piece don't just think because it's a 32/36 it will work well.

 

A bit late on this one, but just for giggles I'll bring one I did up. I Okie-rigged my first weber by drilling and tapping the manifold, really ugly, but it worked. Second mod attempt was milling the manifold and welding in a plate to match. Both got the job done, but were really a waste of time.

Your best bet, not bang for the buck, is an aftermarket manifold. Offenhauser and Cannon made good pieces. One of those companies (offenhauser I think) made one with a split level runner that isolated the primary and secondary carb barrels all the way to the head. That split mani was great for driveability, Heloed with torque and mileage, but performed about the same as the stock maifold. The best, in my opinion, was the offenhauser open runner.
LC Engineering had a line on the Cannon manis. Better than adapters in any case.

You can still find these manifolds in minitruck events swap meets.