'77/'78 might have been the first year. My '83 and '84 has it under the right side (from rear of motor), '91 too. Could probably install an elbow like your '84 had. If it's not overheating, might want to just change out the impeller, put in a t.stat (or insure it's working), and run it. The t.stat would be down there on the bottom like on your '84, but the t.stat cover not quite as reliable IMO -- lower left at spring is under tension, but no bolt.
edit. Did you mean to refer to the lower unit or to the pan under the powerhead (left side)? not sure where the '77 tell tale was routed. could have gone around the back and out on the lower left pan/lower cowling.