I think you need to re-think the membership picture (I still can't fathom why this site seeks them) if you want to complain about being tricked into an untoward photo shoot in boxer shorts, etc. Just sayin'.
If your post had gone onto say that they photoshopped your head onto someone else's nude body, then I'd say you MIGHT have a point depending on precisely what the contract says, but ... you didn't.
Reputable talent agencies don't limit ads to Craigslist (if they use it at all), so you also may in future want to do other checking out of companies before responding, and even more before agreeing to X. You should also do due diligence to know what the market rate in your area is for "catalog photography" or any other kind of model, and of course take particular note of any "up to" phrase and some outrageous higher-end hourly rate. NE isn't a hotbed of fashion photography, and $400 an hour doesn't strike me as remotely plausible rate for non-"uncomfortable (in hindsight)" pictures.
Sounds like you saw what you wanted to see (whether someone had professional signage should be the least of it).
You've also learned the important lesson of insisting on an exact duplicate of whatever it is you're signing and, if there isn't one, you say "Excuse me; I need to go make a copy of this."
"In retrospect I am uncomfortable with many of the items they had me model."
I'm sorry, but ... while regrettable, I don't see any legal argument here.
"But now I am wondering if there may be a legal way for me to return the money and WITHDRAW my agreement to have my photographs published?"
I don't see it. That's something you could easily cough up that $1600 to have an attorney (you also haven't checked out) mislead you and say "Sure! Just give me a $5k [or $10k] retainer." I don't mean to be harsh, but ... this is real world stuff.
"Perhaps due to the presence of tequila shots, which they insisted I drink non-stop throughout the shoot?"
Seriously, don't even go there in terms of excuses. Like your mom may have said ... "If someone insists you ought to jump off a bridge, you'll just ... jump?"
"Or the fact that I signed the papers BEFORE I understood the borderline-pornographic nature of the content I was about to be involved in?"
But you weren't forced to do whatever you were told even after you signed the document; the world wouldn't collapse and there's no gun to your head. Had this agreement by some chance even said anything remotely like "you have to do what you're told, no matter what ... there's no turnin' back or you'll owe US money!" that doesn't mean you couldn't tell them to "Pound sand. I won't do that; pay me for the time through this moment and we'll call it even."