Who,me you say you would like to find a small vacuumm guage to fit for a driving aid.Might I say I have found that a large face guage is more useful than a tiny one that strains you to see small changes.
I once had a 67 Impala w/327 that a PO had installed a commercial guage in a pod about the size of a Sun tach on the upper left corner of the dash.That was one that I could use because location and size made changes visable without having to "look for it".One factory installed on my turbocharged F85 olds was a compound guage showing boost and vacuum but was mounted on the console and was less usful.Bigger is better.
Care and a good feel is called for when using a vacuum guage to set timing because of different timing setups from the factory.Static (idle) timing changes effect the timing over the whole Rpm range and when the advance mechanisms come in action the timing can be over advanced for the conditions.Remember what Jerry said about the detrimental effects of over advancing when looking for max power and RPM.It WILL limit you.
In my opinion using a vacuum guage to set timing is an approximation and not as good as a timing light if the engine is near stock.If modified with cam timing change or compression change then all the factory standards are just a reference point to work from as you arrive at a spark management curve that will give you the best performance.For sure if you just advance the static timing after a cam change to restore proper throttle response you will be over advanced when the advances are all in.
