Old servos

Nick- Prolly Futabe S-48 vs S-4B. Very common and widely used. If they have the old G style connectors (wires exit plug body 90 degrees from the pins) you can cut them off and replace with the newer J type (or use adapters - Cermark sells them among others), and they will be almost universally compatible with newer Futaba Rx's and other brands. The center pulse width is a bit shorter than what has become the standard these days, 1.35 ms vs 1.5 ms, IIRC. No problem in most applications - it just means that when you center your controls mechanically, there will be a bit more full throw available in one direction than in the opposite direction.

Abel

I've got three of them in one of my planes, dont't remember which one! Changed the connectors and they work fine.

S4B was a Controlaire servo. If it has four wires, it definitely is Controlaire and will require a center tapped battery supply. Additionally, some of their servos where negative signal pulse which is not compatible with todays positive signal systems. These where made by World Engines in Cincinatti. If your project is a plane, use a newer servo.

The new Futaba 3004 is awfully hard to beat for price/performance.