Alt conversion/ tach question

All you Guys that have an alternator conversion, what do you now do for
a tach?  I bought one on Ebay from a later car thinking I could just
hook it up and toss it in the hole, but realize it's a smaller diameter,
so whats the next move?
 
Mean while I have a aftermarket hooked up and mounted under the dash so
I can keep tabs on what Im doing, but I don't really want to leave that
in the car,, its fugly!