If you're having the PCM tuned, have the tuner change the high and low tach resolution to 3 for both fields.This will make your tach work without having to buy a converter. It will get the tach within 100rpm of what it should be reading. Down low its dead on, but above 3500rpm its off by just a hair. ABS, speedo etc all work if you just match all the circuit #s when wiring. My speedo reads 2mph higher than what the PCM says, but that can easily be fixed in the PCM. I'd rather have it read high tho as I have a heavy foot...
Wiring shouldn't be a problem. Just match circuit #s, if it doesnt match, do not hook it up. Everything worked flawlessly on my swap besides the fuel level sensor as the PCM handles that completely differently between OBS with OBDII and NBS.
Old: 1998 K1500 White ext cab stepside, vortec 350. Stock besides Volant intake.
New: 1998 K1500 with stock LS2 besides LQ9 truck intake and 8.1L Marine injectors. Dynotuned, 350rwhp, custom 3.5" exhaust, '02 F-Body Racetronix fuel pump setup. All wiring, exhaust, motor brackets done in shop.