I did it for the same reasons you want to.  The full clusters were too expensive, and I did not like the gauges.  I used Autometer gauges with simple black faces.

I made a rear backing plate from 1/8" thick aluminum.  The plate bolts to the back of the bezel and provides a flat surface to tighten the gauge brackets to.  I took the bezel and used a die grinder to enlarge the holes until the gauges just fit.

A couple of tricks are to make sure to use tunnels for the indicator lights like the stock cluster, otherwise you get light bleed and it looks bad.

I just reworked a stock cluster harness and used the stock wiring and the Autometer senders.  Works quite well, and got the look I wanted. 
 

I installed Auto Meter gauges in my 66. I used a dremel tool to enlarge the openings being very careful not to go to far. The plastic mounting brackets wouldn’t work so I fabbed some from aluminum flat stock. I bought a 12 pin prewired connector and wired it so it can easily be removed.

5" speedo and tach, 2-5/8" for the others.  The gauges fit in from the front of the bezel, not behind.  You can use the smaller gauges and have to grind less off the bezel, but I looked at both. and ultimately the 2-1/16 gauges just looked too small for my taste when sitting. next to the 5" gauges 

Like BillyC, I started with one of the plastic backers, but it was a joke and would never have worked, so I went aluminum.