Some came with a factory tach, but for the most part, its an expensive conversion because they are fairly rare.
Super easy to wire up an aftermarket one. 1 wire from teh distributor, an ign wire, ground, and illumination (tap in at the stereo, no searching then).
I bought a cheap a$$ one, but it works. The needle doesn't light up at night though, so its not that easy to read when its dark. Only the backgroudn lights up :/
BUT, the price was right, about $40. I got the summit brand one, but can't find it online. A basic sunpro or auto parts special will do the job, just not the best necessarily.
I have a 3 3/8" 8000 RPM one. I got the 8k because the are the most accurate in teh middle, and once again, the price was right. A 5k would do it, hell, my truck never sees above 4k.
I mounted to the drivers side windshield pillar using the trim piece screw hole. Mounts about 1/4" off the dash, in the corner there after i bent the bracket. No drilling into dash, good visibility. Just bent the bracket they gave me to work.
Wish i had a picture. But pretty self explanatory.
Scott has his mounted in teh same place, maybe he has a pic.
Search, lots of ppl have done different things, but i liked this setup the best.