+1 for it being an Attaque
+1 for a good boat. It will take lumpy stuff like it's on a calm pond.
I have the predecessor - the "Seasafe" - same idea but no drain well and thinner transom (so less Hp cpacity). Yours was what evolved into what they now sell as the O-Pro. If you give Humber a call Sue(assuming she still works there) was really helpful getting me engine weight / Hp specs. Without a serial they may give you the "worst case earliest model" spec, but at leasy you know you wonlt rip the back off!
Mine the serial number was on a screwed on plate- do you have 4 small holes in a rectangle somewhere on the inside of the transom? (probably about halfway down, Stbd side - that's where mine was screwed on.
What you planning on hanging on the back?