When I mulling the pros and cons of the MSD vs. Mallory dist. upgrade, one of the questions I had was if anyone had tried to install an electric tach in the stock 'bird bezel. I really wanted to run the MSD, but did not know if an aftermarket tach would fit in the dash. I just finished the install of mine and wanted to post pics just in case anyone else needed to do this.
I used a Mooneyes 3 3/8" 0-6000 rpm tach that is made by classic instruments. I painted the needle flourescent orange to match the factor gauges and it blends pretty well. I am sure that classic could custom print a gauge face that would match even closer (checked with them and the do custom work). The gauge must be cut apart to fit in the bezel but this is relatively easy if you take your time. The only problem I had was turning the prtective glass face down in diameter. I taped the faces of the glass and used a bench grinder at a very slow speed to do this, but I think the cost a glass shop might charge for this would be worth it. After the cutting grinding is done, the gauge slides into the bezel and is retained by the factory screws. The supplied hold-down brakcet must be lengthed and it installs in the dash as the stock one would.
If anyone needs more info or pics please ask.