Step 7: The finished product, installation notes
The chain arrangement was taken from my research and it seems to work really well for keeping the swing upright while providing maximum support to the seat area. I'm happy with it, although it did make it a fair bit more complicated to hang the swing in the first place.
I also used 4 porch swing supports. Normally they're sold in pairs for use 2 to a swing, but I thought this worked better. They're rated at 250+lbs per support and they're put into the rafters in the porch ceiling so they're not going anywhere.
My estimate is that the swing can probably safely support about 700-800lbs. I've loaded it to 600lbs without any problems and really, it's plenty strong enough to handle 2-3 people of any normal-ish size. At this point it's also been in place and in use for a little over 4 years so I'm pretty confident about its sturdiness.
Oh, I did add some extra supports at the bottom. If you look closely you can see angle braces running along the bottom of the main supports. Strictly speaking they're not absolutely required, but after spending all that time building the thing I decided to err on the side of safety so I added those on before I put it up.