It's handy this because you've seen the thing from scratch and I've got the complete thing so we can help each other out!
That is the only thing I could think that would give you more valve throw as well.
There are only 3 things. The offset on the eccentrics, the length of the slot and sliding block in expansion link as you said, and the length of the bottom lever on rocking arms.
I think that should do the trick, it'll be a matter of timing now. Fingers crossed.

With regards to putting the oil holes in rocker arms, I presume you can get under the boiler with the oil can, in which case it be a good idea I guess. Will check if you like.
I was looking at the lubricator, I found an old file the other day with some scribbled notes. I don't think it gave enough throw on the lubricator. There isn't much soace for the arm to move on it, from one extreme to the other it only gives 1 click on the ratchet on mine, so maybe it needs a ratchet wheel with more teeth if I can't get it to throw enough. The problem will be if you get too much throw it will foul the frames etc, but not enough will not be enough to turn the wheel!
does your axle pump have a by pass valve anywhere in the plumbing? Mine doesn't but the bore seems tiny so maybe it's assumed it just needs to pump all the time? Seems strange not being able to adjust it though.
Good luck.
Nick