A couple things you need to ask yourself are 1) what do i want to do with this and 2) whats my budget.
The quickest and easiest is to hop on Team Chevelle and find someone there who is doing a 4speed manual (usually a Muncie, but sometimes a T10) to overdrive swap. Hopefully they'll also be removing the clutch linkage and you can pick up almost everything for about a grand, trans included.
The stuff that fits best is the OEM stuff from the factory cars. The reproduction stuff probably fits the bill, but it can take a lot of rework sometimes to fit properly.
Im sure one of the catalog companies has a 4 speed install kit. Youll need a bellhousing, gearbox, shifter, shifter linkage, clutch, throwout bearing, Z-bar, pedals...oh and a flywheel installed on your motor amongst other things.
If you're running a stock motor, or mildly warmed over, a stock M20 will fit your bill just fine; has a 2.52 1st gear and you'll need a 3.42, 3.55 or 3.73 rear axle gear.
A 72 Chevelle would have a 26 spline input and a 32 spline output, regardless of the ratio of the Muncie (M20, M21 or M22). This also means you could use a Super T10, Id recommend a 2.64 1st gear or a 2.88 1st gear. For the 2.64 1st, Id recommend the same rear gears as the M20, for the 2.88 1st I would use a 3.23 or 3.08 rear gear.
If you try to use a 27 spline output Muncie or T10, you'll need a new driveshaft and have to modify the shifter/ shifter bracket to make it fit in the console (assuming you have one)
Aftermarket Muncie with M22W or M22Z gearset
Doug Nash 4+1 (Richmond 5 speed)
Id open a second thread over on the Team Chevelle manual trans webpage; according to Jody over there, the later chevelles can have some unique requirements to install stickshifts. Ive never put one in a later chevelle, although several of our customers have.
Keep us posted!