Archimedes Penta Outboard Manual
Is it definitely an Archimedes Penta? My knowlege of Archimedes is very sketchy, but Archimedes (without the Penta) go way back in outboard history) and orignally made two or three sizes of horizontal twin.
Through various takeovers (Electrolux etc.) the Archimedes name survived and I think got combined with Penta in the late '50's or early '60's, though I don't think there were any horizontal twins by this time. I had an Archimedes for a time, whcih I recall I dated to around 1940 - I suspected it was around an 8-10HP., and was as much as I could do to lift the thing! 
I did have some basic adverts for the Archimedes range - I'll see if I still have them and let you know. Good result with the SD though eh? You'll have to let us know when it fires up!
The pics are of a 'Type B-22'. I have two, to make one good and one fair to middling later. Barrels are weakness! Else very rugged! I believe it was 20Hp. I would love some more tune up info if any one can help.
Archimedes Penta Outboard Motor
Volvo Penta (Formerly Archimedes Penta) Outboards. Outboard Engine Manufacturers Boat Part Manufacturers. Volvo Penta (Formerly Archimedes Penta) Outboards.
Free Outboard Manual
It is bloody heavy, both to lug about and pull start for a small bloke like me.. The blue one fires up and idles but has one cracked block, hence the other for spare bits. PS: Do not forget the SD magneto numbers for Charles! He is challenged in that need as we all know.