You certainly want to make sure you buy the correct gasket with the front seal thickness that matches whatever oil pan you have.
Not everyone is aware that Chevrolet changed the front seal radius on the small-block pan in 1975. All production pans prior to 1975 had a 2-1/4" seal radius, and used the "thin" (0.22") front seal. In 1975, the production pan seal radius changed to 2-3/8", and they used the "thick" (0.41") front seal. At the same time, ALL Service replacement pans manufactured after 1975, regardless of their intended application, got the 2-3/8" front seal radius and require the "thick" front seal. Fel-Pro (and others) who make the molded one-piece pan gasket have two part numbers - one with the "thin" front seal, and one with the "thick" front seal. If you use the gasket with the "thin" front seal on a pan that requires the "thick" front seal, it'll leak oil like gangbusters, and you can't stop it. Measure the pan before buying the gasket so you get the right one, per the photo below - you can't take a used one back.
Another great source for front leaks are the cheapo chrome Taiwan timing covers with the front seal flange spot-welded on; the production covers had the flange roller-welded on for a perfect seal, but the Taiwan geniuses didn't know why, so they took the cheap route and spot-welded it. Result? Leaks.