PS: That's a hell of a rack, haven't seen that one before. Dig it so far, ditch the blinkers for some small ones, makes a world of difference.
Additional on head choices: you can use the big heads, just takes a few minutes with a belt sander to grind the fins down enough on the offending side.
Vespas do have as many choices as almost any brand out there. Polini's are fast, but a proper case match leaves just a sliver of sealing surface around the transfer ports, at least with a kinetic case, DR may be better.