Hi James,
I can't answer your question about 8 hp engines, but on my last Tohatsu, I did have a single lever that controlled both the direction and throttle.
I haven't bothered to fit to the new engine as I didn't really need it and I am not sure it would work anyway.
Pictures are much easier to explain/show but I have no real idea how to upload them here - I have made an attempt!! Didn't work
If this does not work I could send them direct.
I can't find your details in the handbook but if you would care to send me your email address I will let you have them.
Best wishes