Welcome knightfighter5, you have a superb and desirable boat with your Seafair. I believe the early ones were made with a head, but that was outlawed from around 1960 unless a holding tank was installed.
There are members here who know everything about Seafairs, give a few days and you will get your answer.
What engine does it have?
The early ones had a head as an option, but mine did not have one. The motor on it is the original 75 HP outboard as it is the only holes in the transom. Now, the bad news. Every inch of transom, stringers and floor is dry rotted to nothing and the motor is trash. The fiberglass is in fantastic shape for the age and condition of its backbone. Back to the date thing, the Ohio tag that is affixed to the hull also lists it as a 58. Being that is the time the dealer first had it had registered in their showroom. I just wish I knew how early mine was. I guess I will just have to settle in knowing this was one EARLY Seafair!
They have guys doing exactly what you need to do with the wood stringer boats (not uncommon) ... They have lots of threads with pictures of how they did whatever and good discussion of materials and techniques
they also have a forum for factory serial number plates and deciphering them, so you'll get more info on the actual build date
The Seafair sedan was introduced in 1959. But that is the 1959 model year which was (like automobiles) from Sept to Sept. Glasspar had production boats in the dealers showrooms in Sept of 1958. So if you bought one then, it would be titled in 1958 but it is a 1959 model.
Note: Here is a copy of the press release for 1960 which states that models will be available in September (1959).