Yeah, it sounds like you're interpretating that right. I can understand why they are not allowing movement of the wishbone bases since doing so would encourage people to completely optimize their geomtry which would result in cars that aren't really in the spirit of the originals.
You can get over that though, by having a clevis at the upright. It requires either modification of your existing upright or a new upright, but fabricating a new one from sheet metal with a turned bearing cage isn't *too* much work. Sorry to use Formula Student as an example again, but here is an illustrationn of what I mean:
Those aren't fabricated uprights btw....they have a sponsor that casts stuff for them!
If new uprights are off the options due to rule restrictions, then I think it would be fair to say it's a good justification to perhaps using a threaded rod end on the top link which isn't so bad. It's not loaded as heavily as the lower link, and it would give you the adjustment you need which will outweigh any weight penalty you'll have from a large rod end.
If you've got the time, the rest of Pat's colums on the
Formula Student Germany website are a good read. I think there are about ten or so now. Just search through the news blog and you'll see them
I do like Gorans solutions as well, and that's another option. The thing to do would be to compile a few pictures of various designs and then see which is going to be the most suitable for your application given the size of wheels you have, the layout of the existing geomtry and the upright design. At the end of the day, if you designed some wonderfully engineered upright that avoided using any threaded rod ends at all but was a complete pig to adjust and resulted in you just leaving your settings the same between sessions, then you may have well have just gone for a slightly less elegant but more more easily adjustable solution. Good engineering is as much about compromise as it is about good design!