Correct, it is a 1976. I may be wrong, but I think it might be a commercial model. Don’t worry about the gearcase, it’s just a regular unit used on the 22 cubic inch motors for a long time, with added ears. In fact, they put it on some American motors for awhile–till everybody sawed them off. Use the parts list for the 1976 25hp for that. Carb kit?? That, I hesitate to speculate on, but again probably a stock carb of the era, unless they had the nerve to put the carb of bygone years on it.