I have a 55 Merc with the tea pot and wanted the new 390 CFM Holley.  I did not want to buy a B manifold because I am still thinking about the Mummert manifold, even though I like a stock look.

I bought the 390 Holley and a Trans-Dapt carb adaptor (#2064) from Summit.  The adaptor comes with the holes cut in at the tea pot bolt pattern but the holes are not drilled all the way through.  I then purchase allen wrench driven bolts.  These were flat topped with a 45 degree angle from the edge of the head to the shaft.  I then had the machine shop drill the holes with the 45 degree taper so the head was slightly counter sunk and the angle of the bolt head matched the adaptor. 

The adaptor was then bolted to the manifold with the original spacer in place and the Holley was installed on the adapter.  The original throttle rod fit perfectly into a hole on the Holley but the clip that held it on the tea pot did not.  The machine shop drilled a small hole in this shaft for a cotter pin to secure it in the linkage of the carb.

My oil bath was dried out and dust and crumbles were falling out of it.  I reused the oil bath by using someone elses idea from this site.  I cut out the guts that are attached to the top lid of the oil bath, put the base of the oil bath on the carb,  then installed a 9" chrome air cleaner inside the base with a wingnut to secure, and finally put the lid over the after market air cleaner with its own nut.  It is a good paper element air cleaner inside but appears to be the stock oil bath on the engine.

I hope this gives somone some alternatives for a carb upgrade without a manifold change. The change to the new Holley is like night and day over the tea pot.  The adaptor costs about $20, bolts were $4, and the machine work cost $10.  The other adaptors I found on the internet were about $90-100.  At that price I would have bought the B manifold off of Ebay.