Looking at putting adjustable outhauls on my booms. Can I use the extra pulleys I have on my boom end instead of the floating pulley in the above diagram?
The extra floating pulleys are useful, they transform a 4:1 advantage into an 8:1 advantage.
Makes tightening the sail much easier, especially in a gust (which is when you need it).
I tried 4:1 but it was woeful, 8:1 is the go.
Yes, that's what they are there for.
Oh hang on, I just read it properly. Those 2 'extra' pulleys are really the same as the single one shown at the boom end in this diagram. You won't be able to fit three loops of line through the ones in the end of your boom, so you use the 3 separate ones.
Those floating pulleys in that diagram (that you are talking about) are also a convenient way of having a bigger/decent diameter rope to use to pull on the outhaul. The rope in those cleats is 8mm or bigger I think.
If you used just the outhaul rope itself it is going to be a bit narrow to get much leverage on, plus as Nebbian points out, the ratio isn't going to be as good.
If you want to make it really easy you can also use a harken (?) block on the end of the sail to give you even less resistance.
It is easier to just buy the Chinook kit, and if you need to modify it, you can then change it later. I don't think the kit is that expensive.