According to what Mark said about the indicator holes, they're 5/16"...I did a swap to my '84 Mustang several years ago using Painless warning light indicators which are available in 5/16" diameter-they're about $7 a piece from Summit or Jeg's...and they're easy to wire in.
I'll try to take some pictures when I get mine and start prepping for install. I'm sure there are a few folks that will beat me to it, but if there aren't any and I'm in process, I'll take a few and post up. I know I need to either repair or replace my dash pad anyway...probably should pull my heater box down and reseal it too.
Anyway, here's a couple of the indicators...
Green...
http://www.summitracing.com/parts/PRF-80205/
Blue...
http://www.summitracing.com/parts/PRF-80206/
Amber...
http://www.summitracing.com/parts/PRF-80203/
Red...
http://www.summitracing.com/parts/PRF-80204/
