@Ross ********
IF you don't have an extensive history of living here on back-2-back 30 day visa exempt entries or 60 day tourist visa entries you shouldn't have any problem stamping IN to thailand.
I think you might have more problem with your air carrier because you're comin' to thailand without a visa (entering on a 30 day visa exempt stamp) and your proof of onward travel is longer than 30 days out (the time you'd get stamped in for).
I'd call your air carrier and see if that's gonna be a problem or not. If they say no problem you won't have a problem getting IN to thailand when you fly in OR when you try to re-enter after your time in Cambodia either