Still can't find the model #

[schuder]

I have a 1959 35hp super seahorse, I see all these models. RD-RDL-21
RDS-RDSL-21 But I don't know how to know the difference between all these models. What do all the letters mean?

 

[F_R]

RD is manual start. RDL is manual start, long shaft. RDS is electric start. RDSL is electric start long shaft.