As already determined there is no provision for a cable drive tach for the A models. I have seem electronic analog tach's offered on the web, can't find anything suitable on a quick search.
The redline for the A model engines is the same as the manual trans engines, 10K. I have heard of a couple CM400A's that legitimately hit 100 mph, one had a ticket to prove it.
Changing the carbs has been done, using the smaller VB22's with 30mm venturi's, and it was a fail. Loss of torque. Now, I can't say for sure this is not a way to go because the people who did it weren't well versed in carbs and IIRC one used pod filters.
I do know that a head swap to a manual head doesn't work because the combustion chamber is larger which lowers compression. I don't think anyone has tried a cam swap using the manual trans cam, that is a possible experiment someone can try.
One simple thing for anyone is port matching and intake port clean up. If you look inside the ports you will see the casting seams that protrude into the port, grinding those away can hurt. Port matching is just a case of mounting the insulators and grinding away any of the head the protrudes so there's no ridge.
You can see the ridge at the end of the red straw
This is after some mild grinding
Don't bother smoothing out the rough grind marks, those actually help creating turbulence which keeps the air/fuel mixture atomized.