Quick way to check - if it's got the small bumpers tight to the body, it's a 72. If it's got bumpers that extend out from the body with black rubber covers (5 mph bumpers), it's later - they started in '74.

Similarly - do you have cats? They started in 75.

72 has some interesting pros and cons, and is probably faster than the 77 (due to the latter's emissions controls. (My MIL's 72 450SE is quicker than my 76 SLC.)

Even if it is a 350SL, it has a 4.5 liter engine.