You definitely should try it when you are here in Florence! Go to the Mercato Centrale, there is a place called Nerbone's, really popular, that is only open at lunch and serves great "panini" with the trippa and lampredotto (separately, not together).
I've never tried making it, so I don't know how hard it is.... I went in search of a recipe - many are in Italian but I found this one in English: Fork Spoon Knife: From Florence!!! Panino al Lampredotto by Juls
Ciao a tutti!
you might also try both Lampredotto & Trippa at the peddler between Via Dante and Via de' Cerchi or....this little trattoria which is really one of the best renowned by locals: TRIPPERIA IL MAGAZZINO in Piazza della Passera, an authentic quaint little square located in the OLTRARNO district. It is mostly frequented by locals. Only humble and tasty recipes from the Tuscan traditions are served with a great glass of CHIANTI red wine! Buon appetito!