Need help identifying seagull model w/o serail.

[Winfield]

Hi there Seagull people of the world.

I have recently obtained a small sail boat (Dutch kolibrie 560) and am in need of a motor.
The kolibrie company website states that the boat requires a long shaft with +/- 4 hp.
People have suggested getting a seagull because of its durabilty and I have been scouting Dutch secondhand pages for one.
Today I found an advert of a model with a decent pricetag and it is supposedly in great condition but I am having trouble finding information about its horsepower and shaft length.
The seller was not able to give me a serial number so I was hoping that some of you would have the right expert knowledge for telling me some of its specifications or even a modelnumber.
This is the advert link below containing some pictures in decent quality.

http://www.speurders.nl/overzicht/seage ... &order_by=

I hope one of you can help me with this, I was asked to notify the seller on short notice (today) wether I would buy or not.
Thank you in advance!

-P.Winfield


EDIT: I have found the serial number, it is: SJP 27736
Can somebody help me with specs on this serial? I'm getting all confused by the tables.

[THCL500J8]

Series: The Forty Series

Manufacture Date: 1960 to 1961