There is no "sending unit"- - -the gauge reads pressure directly by a small-diameter tube to the gauge. You can get a gauge for a GMC dash cluster that has a max reading of 60 PSI, which is what most people do when going to the high pressure engines. Just changing the gauge face does not solve the problem- - -the needle will still max out, regardless of what's on the gauge face. Some of the "new" high pressure gauges offered by the resto-ripoff guys have problems with leaks and/or inaccurate readings- - - -probably made by some 12 year old kid in China!
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!