Looked it up for you and all. NAPA p/n 30910, mfg by Kat, $68.49. Short stainless immersion heater with cord.
http://www.napaonline.com/en/p/KAT30910
Starter on the 8.3L is way oversized to begin with (same starter used on the Cummins 855 based NHC 250, just different pinion), so it can crank well even in cold temps, as long as batteries are healthy. Oil heater will not really warm the engine much for better starting because this heat just sits below the oil pan gasket, but it will allow the engine to develop oil pressure much faster after initial engine start up. Will also reduce condensation which can form inside the engine if the engine is only run a short time after the cold start.
Additional info:
For best success cold starting an 8.3L, below are my personal recommendations, in order of priority:
1. Make sure your fuel system is air-tight on the suction side. Filters, hoses, lift pump, tank dip tube, fittings, etc, are clean, new, and tight.
2. Be sure your batteries are up to snuff. This means they are less than 5 years old and test at least to their rated CCA value (load test with a test result value, not just "passed", or measure internal resistance which calculates actual CCA remaining vs labeled value).
3. Though many are against it, the stock ether system works great on these trucks. It can even compensate for weak #1 and #2 above, but should not be used for those reasons. I try not to use it, and can tell in the first 5 seconds of cranking if going to be needed. I use it based on whether I feel the engine will start or not within a 30 second window of using the starter (starter use limit before 2 minute break to repeat). If the engine is not beginning to kick off on several cylinders by 10 seconds of cranking, I will hit ether while cranking (the only way this system works anyway).
4. Fuel is winter type diesel, meaning it has anti-gel in it. I have not personally had an issue with waxing, even using summer fuel in winter, but still good to try and be attentive about it if you want your truck to start reliably on no notice in the winter. I did have ice plug my large frame mounted primary filter because I left my tank level sending unit out for a while, uncovered, and snow fell into fuel tank. My fault, and filters did their job. Removed them, defrosted, poured water out, refilled them with diesel, all set.
