welcome. if the outdrive is original to the 1974 boat, than it is a 270, 275's didn't come out until the mid 80's.
Either way, the oil change is pretty much the same. I use a standard lower unit oil pump to do mine. remove the top screw, which has a dipstick attached to it. remove the drain plug at the bottom and drain the oil. then using the pump, pump approximatly 2,5-3 quarts of motor oil up into the lower drain hole. check the level using the dipstick. as long as its in full range on the dipstick your good to go. replace the orings on the two plugs.
