On the subject of lifts and lazyjacks interfering with the camber of the sail, I rather agree with Arne that it probably doesn’t matter much, in practice.
When I made my rig I did worry about this, and I think I have been able to reduce that interference to some extent – for what it is worth. With a split junk rig together with Slieve’s sail catcher, lazyjacks can be left out of the rig as redundant. The lifts are in two pairs and attach to the top edges of the sail catcher, supporting the bundle by way of a batten along each top edge of the sail catcher.
The forward lift pair can be placed up and down the mast, where it is in the slot and does not interfere with the sail (and is out of sight in the photo below). I would expect that the camber at the fore part of the sail is the more important to be protected. Anyway, with the SJR neither the jibs nor the mains need be interfered with by the fore lifts (which are in place of the so-called "mast lift".)
The only remaining issue is the aft lift pair. (These replace what some people like to call the "topping lifts" but actually they are for a different purpose.) This pair can potentially interfere with the sail but mainly out near the leech where the camber is least – and can be placed as far aft as possible (consistent with them not being able to get on the wrong side of the yard when raising and lowering the sail) as seen in the photo above.
Another potential mitigating factor is possible with respect to the aft lift pair, and that is to spread the two support battens which support the sail catcher, by means of a hairpin joiner at the front, and some sort of equivalent at the aft end which does not foul the sheets. You can get the idea by looking at the hairpin on the front of Amiina’s sail catcher. I never got this figured out properly and decided it wasn’t worth the effort, but if pursued, spreading the sides of the sail catcher a little will give a little bit more stand-off to the aft lifts, so that almost none of this rigging should interfere much at all with the sail. As I said, I don’t think it matters enough to be worth the trouble, and, as a matter of fact, the sides of the sail catcher seem to spread themselves to some extent anyway, as soon as reefed panels and their battens fall into the catcher.
I think Serendipity’s simple 2-pair lift arrangement, with sail catcher and no lazyjacks, is (for the SJR at least) about as simple an arrangement as you can get, and with minimum interference with the sail camber…. for what difference it makes – which is probably not much. The SJR and sail-catcher is a delightful arrangement in my view, but mainly for other reasons.
Its wonderful to see Arne's photos of sailing right now, in a nice breeze. I'm envious!