Great rescue! Forget about the 60 as it is not wide enough. Most vieja reach 10-14in, Syns being one of the larger growing types. From the description of the seller, he doesn't sound like the best fishkeeper around. Its possible the your syn will max out on the low side of 10-12in. Sex of the fish also plays a factor. 100gal might get a little cramped with the O and syn, but give it a shot and see how it plays out. You'll def want to stay up on your water changes.
BTW, the syn looks great. Nice sharp colors.
