Hi,
I forgot to mention that i had made this very thing back in the early 1980's, but i forgot what the part number was for the frequency to voltage chip. It was something like 9400 or something like that, and was fairly stable for that kind of device back then. I was able to get about 5 digits, but the stability of the rightmost digit wasnt super good and would change quite often. It will probably be good enough for your app though.
Oh yeah, the way i did it was to simply use a frequency counter with the v to f chip, an 8 digit unit i had built out of discreet 7400 family counters and latches and other devices. The LED display was rather smallish, but it did the trick. I actually still have this thing around (the chip somewhere too) and just checked it the other day to make sure it was still working (i needed a crystal controlled output from it for testing something else too).