Wow, I don't understand how you ended up w/ a shortage on SP prospects (w/ 15 keepers to start from), if that's really what you wanted, but I'm currently doing my 10 keepers w/ the Dodgers for a very similar kind of league.
I agree w/ the last few posts that I would not deal Guzman for most any SP prospect, especially given your 6x6 format (just like ours). And would only give any consideration at all for the likes of Cain, Billingsley, Verlander, etc. I wouldn't even do Liriano or McCarthy -- I need to see more proof from Liriano given his history, and McCarthy doesn't seem to have the kind of stuff to put him up there although he may just be good enough anyway (and I do own him in 2 other leagues). Baker's not even worth mentioning, if you mean Scott Baker.
Guzman might not stick at SS, but he doesn't have to -- and it doesn't seem like his defense is no good from what I hear, but rather, just people's concerns about his size. Heck, Guzman probably has way better shot at sticking w/ SS than BJ Upton anywhere in the infield.
If Jeter and ARod stuck at SS like they did, I'm not sure why a guy an inch or two taller shouldn't be able to given that he's supposedly decent w/ the defense -- probably better than Jeter was in the minors, if I'm hearing right.
I don't wanna say too much since a few others in my league are reading this forum (including prhood higher up)
but suffice it to say stick w/ Guzman unless you're getting King Felix in the deal.