So what's special about a 327 ??? All depends who you talk to. As bucket say, it does fit that time period. However, some don't kmow the difference between 327's, Thru 67 the 327 is a small journal crank just like the 283. In 68 and 69 the 327 went to large journal which is the same as the 350, hence 68-69 327 blocks are the exact same block as the 350. They are identical blocks and in those years, even share the same cast #'s. So if you get an engine with the 68 or 69 350 cast #, it could actually be a 327 and vice versa. The advantages and if you want to run the 327, you'll want the small journal 327 since its not only year model corret for your truck, but both small journal engines, 283 and 327 are forged cranks. All of them, not half of them, or only truck models, or engies in front of manual transmissions, but all of them. Many think the smaller journal is weaker cuz its smaller. NOT TRUE. The small journal 327 is turning a smaller mass. If you took a large and small journal 327 in exact same set ups as far as cams, heads, car etc, the small journal would win a 1/4 mile race. Only 2 reasons and it wouldn't be by much, but just enough to make a difference. #1, less parastic hp loss to turn the rotating assembly with less friction drag of having smaller bearing surface. #2, the small journal will get the rpm up quicker and the small journal will turn a higher rpm too. Even in a 2 bolt main block since small journal was only available in 2 bolt. Again, smaller journal, mean less strain on the main caps, and the forged crank is not likely to flex either.
Ok so with all that..... Good Luck finding a small journal 327 and if you do, be prepared to pay big bucks for it. Honeselty, you can probably find a 5.3 LS engine for cheaper than you can find a SJ 327. The last 327SJ long block I seen on CL, the guy was nuts and wanted $1000. I love the old shcool idea with that truck, but you mentioned it yourself, I'd love the LS new school in the old body style too. Realistically the cheapest fatest way to get the truck running, and cloest to old shcool you can reasonably get, is to go with the older 2 peice rear main 350. They are plentifiul, the rebuild kits are cheap and they are easy to acquire parts for quickly. If that truck has the rear end I thnk it does, it probably has a 3.90 gear ratio in the rear end, so an old school 350 with a 700r4 would be a great choice and probably get a litle better mpg than your Squarebody.
I love when my little guys are out there taking interest in what I'm doing. I just have to be careful they don't throw stuff in the direction of the truck 
