That will fit. Remember in '61 - '68, there are just three holes drilled for the radio, rather than a huge hole. Radios were dealer-installed units, for the most part, as were the antennas - one reason you'll see an antenna on the left OR right side of the cowl. My last two '68 trucks were like this. The radio mounting was standard, however.
Bit of trivia you may not know - the same-year Ford trucks used the SAME radio, with a very slightly different chrome bezel being the only difference. So if you are out bouncing around in the junkyard somewhere and a Ford pickup is there, check it for a radio! The 1960 - 1966 Ford and Mercury trucks have the very same radio.
That is a cool option for someone that does not have one. If you have a factory style one, you can have it fitted with modern internals. I had mine done but I skimped on FM which I wish I would have gotten.
I don't have a radio at this time, so I will most likely go with the one from Retro Manufacturing. Had been finishing the wiring with the Ron Francis kit, and have the wires sitting around for the radio, but nothing to connect them to. Have too many other things to do with the truck to mess with getting an old radio refitted with modern guts.
patrick - thank you for confirming the fit and the trivia.
I have the same vehicle and ended up going with a Secret Audio from http://www.vintagecarradio.com. Not sure if the Retro Manufacturing radio will fit but I like my little hideaway unit I put in the glovebox.