I think its much easier to overbluff.. there are ton of FDs.. since I expect him to be pretty loose preflop and call almost any suited hand. With that assumption, hes got 51 possible unpaired hands (incl JT since its a SD OTT). Compared with possible number of 7x - 48 +22 (possible slowplays). Lets assume that half of the slowplays would take a different line, its 51/59 possible bluff:value ratio.
We should also take into consideration the fact that the number of his bluffs is pretty accurate, but the number of value might be significantly lower if he starts folding some 7x OTF or OTT. That said, vs a guy who might be overbluffing by nature and there are prob even more bluffy combos OTR than the value ones in his range, I dont think I am ready to fold any Ace...