Just bought a vintage Sprinter Gran Touring, where to find info?
'Gran Touring' alludes to 'Gran Sport' and 'Gran Turismo'. These were Campagnolo names used in former times for their derailleurs. I am not old enough to remember when those former times were, but they were decades and decades ago!

The brand means nothing if this is a department store bike. That means you have free reign to do what you like with it. You can even get it shot=blasted with braze-ons for those cables if you really wanted. Personally I would be tempted to keep the cables as is but maybe get some proper clips to hook them onto the frame. You can get them from a retro bike specialist, e.g. one that does Sturmey Archer 3 speeds.

The geometry and ride should be good, maybe put the seat back so it is mid-rails instead of inch or so forward. Thebolt holding the seat on should go behind the seatpin, not in front.

I guess you have a non-standard wheel size, treat yourself to some Schwalbe ones to fit, read the ERTRO size off the side and special order from your LBS accordingly. In that way you won't have to pay postage. Modern Schwalbe tyres will be consistent with the bike and be puncture 'proof'. This will make the difference between oddity and everyday utility bike.

Bikes of that vintage had saddlebags for carrying stuff, consider getting one as this will make the bike look better than it is, albeir doubling the price if you get a UK Carradice one.

Those 'Northroad' bars are really comfy when riding in traffic or on bumpy trails. The turning circle will probably be that of a bus with that steering rake so adjust your riding style accordingly.

If you are doing a full refurb then give yourself a whole weekend for re-packing the bearings etc. Some sizes may be non-metric, that might be to watch out for. Given the super paint quality apart from the top-tube scratches you could just ride as is and put some 'One Less Car!' stickers on the top-tube after you have got the 'gran touring' stickers off. Steal some nail-polish remover from someone female if you haven't got any useful thinners for that. T-Cut should bring up the shine on the chrome not that it really needs it.

Very nice find, definitely just a department store bike though, which is good because you can do what you want to it without destroying some notional priceless heritage.