How to add on gauges??

I have a 72 duster, with a slant. (i know..i know.. drop it an sb) anyway..
im keepin the six for a while and it runs great. Just worried about the performance of factory gauges. Im reinstalling my gauges and bezels. But think I want to add a three pak of aftermarket gauges.
(oil,VOLT,temp) how hard is this to do? and how would i do the wiring?

Thanks for any help