Volvo 200 outdrive oil question

[68Donzi]

Just a quick question:

What do people recommend to use for oil in a '68 Volvo 200 outdrive?

I have heard synthetic 40 wt oil. I have a repair manual and it says "same as engine." That's confusing. I can't see putting 10W-40 in my lower unit.

Can the masters out there please let me know what to use?? Also
does anyone know where I can buy the oil injector kit that lets you put the oil
in from the bottom of the unit to remove air? Its a screw in tube that attaches to an oil can but it lets you squeeze the oil into the unit from the bottom drain hole.

Again any help is appreciated!!!

Thank you!

-Andrew