Just finished my weber swap on my stock 86 Samurai.  Other than wrapping up all the unused emissions wiring it was a smooth install and looks fantastic with the stock aircleaner.  The stock manifold holes are slightly smaller than the Weber adapter.  This would have been a major disruption in air flow.  It is important to take a round file and rasp out the manifold to match the adapter gasket.  Don't worry about making it smooth, just fit the adapters with the bolts and mark the manifold material to be removed.

The other restriction I noticed is in the stock air tube to the air cleaner.  It chokes the air cleaner down to a 2" pipe.  Either leave it off or fit a 3" flexible tube back to the battery area.

I will let you know the results in performance as soon as I get the header installed.  Is there a simple way to make sure my distributor vacuum advance is working?

Have you started it with the weber on yet? Reason why I ask is you didn't mention lapping the adapter plate flat. They are usually wrapped and cause a vacuum leak.

Here is the vacuum advance check from the factory shop manual you asked for.

Have you started it with the weber on yet? Reason why I ask is you didn't mention lapping the adapter plate flat. They are usually wrapped and cause a vacuum leak.

Here is the vacuum advance check from the factory shop manual you asked for.

Haven't started yet.  Didn't know about warped adapter.  Cross your fingers.