Rob, each boat is different. Case in point, your end cap.
First suggestion: drill out the rivets, rotate the cap, put new rivets in. Not hard to do and assuming that it's the normal "cap", the rivets don't need to be better than ordinary aluminum pop rivets for the loads. Alternative, if there's a reason the cap won't rotate: rivet a longer strap across the top side of the back of the boom, something like this one (upper right, almost out of the picture):
![2663](./gallery/image.php?mode=thumbnail&image_id=2663)
It has 4 holes, so it doesn't rotate. For this application you mount it at the end of the boom, but angle it
back so the rivets clear the end cap, but the "bow" end is at or a bit past the top end of the boom. Then lash to that. (But only if you absolutely can't rotate that cap).
Third alternative, you can use two cheek blocks (one on either side) to replace the double block.
Next: my outhaul is tied to the clew. My
current setup (which does not use the single block): lead outhaul into Port sheave of double block, run back through clew grommet, into Starboard sheave of double block, then forward. Up to the cleat, the outhaul will be under tension, even if slack, you'll be able to "snug" it without changing the sail trim. No fairleads required. I have one eyestrap at the very front to which I tie a very weak bungee. That holds the tail coming out of the cleat along the boom. You can grab the outhaul tail anywhere and adjust. When done, just let go and the bungee will keep it secured. (Photo above shows the setup before I added the bungee and even with using the boom vang bail, it sags - red line).
I use a rolling hitch (tautline hitch) on the bungee, so I can adjust tension if needed.
I keep my sail on the boom (even when I take the boom off) so all of this can stay in place.