My Reference corroborates Dusty's -- that it is a 216, 1942 to 1951 (in US trucks, anyway)
Before attempting to run it (unless it's already running), you might want to check out our Tech Tip for starting a dormant engine
Other folks on this site have used babbited engines (low oil pressure engines like yours) for daily driving under the conditions you are anticipating for yours, but they do require a little more care and attention than some of the more modern engines do (like regular valve adjustments and oil changes ... and a few other things I can't think of at the moment). Daily use is doable with a 216, but not merely drive, park, repeat.
The best advice we can give you is that if your original engine will run, then get it running well. Get the truck driveable as is. Enjoy it for a season or two before ripping into any major projects. You might find you like it as is ...
BUT ... If you want to upgrade the engine to something that will provide more margin for daily driving (while retaining most of the truck's original "essence"), the good news is as 3B says -- you have plenty of options with a fairly good array of GM six cylinder engines over the years, ranging from the venerable 235 all the way up to the GMC 302. And as he says, some of these engines will require more modification than others.
I think the options fall into three broad categories for the average restorer:Easy
(No mods required) -- Engines in this category include swapping out for another (but better) 216 and the early 261. There might be others...Not bad
(some minor mods required, but still very doable) -- The mighty 235, later 261's (these two blocks are the most popular we've seen for re-engining)Challenging
(significant mods required) -- Later sixes like 250's, 290's, GMC 302 (or any GMC six, for that matter. They're different, rare and harder to find parts for, compared to the Chevy sixes)Advanced/Graduate Level
-- Diesels, V-8's. Sure, you can toss a v-8 in there ... and make all the modifications for it. Many people do. But you can't swing a dead cat at a cruisein without hitting 5 or 6 trucks with v-8's in them. But pull up in a '46 with a two-cycle oil-slingin' Screamin' Jimmy, a Cummins Battle Rattler, an Isuzu Rice Rocket or air-cooled Deutz and you will be a show stopper with your very unique truck. But there's a very good reason for that ...
But to start, here's a couple more Tech Tips:Swapping out a 216 for a 235Rebuilding a 261
-- Although it's an article about engine rebuilding, we do discuss how easy it is to replace a 216 with an early 261.Swapping out a 216 for a GMC 302
A couple of things to keep in mind when pondering (Note, while most of this applies directly to the Advance Design Trucks, it applies to the '46/Art Deco Trucks, too)...
1. Most of the sixes that came after the 216 will need to have their water pumps raised to the higher position of the 216's. This is because of the body redesign that came with the Task Forces trucks ('55 2nd series to '59) that lowered the profile of the truck. They also need the "short shaft" water pump, because of the tight fit between the radiator and the engine. This is why you see a lot of Advance Design trucks with the upper radiator stand bracket cut -- to accommodate moving the radiator to the front of the bracket to provide clearance for the unmodified water pump ... You can just use the new motor as is without messing with the pump location, but this usually leads to overheating issues as the fan is only working on the lower half of the radiator. ... or you can use an electric fan .... which then requires converting the truck to 12 volts as noone I'm aware of sells a 6-volt radiator fan .... One must be careful when chasing rabbits down their holes like this as you can get lost down there
2. The later 235's had side engine mounts in the front. The earlier trucks like yours just had one under the timing cover. This is not that hard to address if you want to use one of those engines, but it is something to keep in mind as a data point for the over all project. I am not sure what the year cut off is for the engine mount dealio ...
3. *Some* sixes will interchange directly with the 216 with negligible modification. The 1954 261, for instance (and later 261's that were molded in the 1954 mold as replacements for the 1954 motors). Others, like the GMC 302, will require more modifications. But if you have the gumption, the 302 is a very sweet upgrade and will get LOTS of attention (and sheer coolness points) at the cruise-ins and car shows.