50 GMC 228 rpm's and tach ?'s

[gmcer]

My 50 GMC has the original motor . I really don't know how far to push this old girl . She runs runs sweet but when you get your foot into it sounds like its gunna blow ! LOL also lack of insulation . what should the rpm's be ? Also I have a suntune tach that I want to install but don't know if I can. There is no switch for 4,6 or 8 cylinder 4 wires blue, red, black and green. usually red power, black ground , green negitive side coil, blue light on tach. the truck has original positive ground system. Thanks for all your help !!! Matt,