If you've just had the engine rebuilt I'd change it at 50 hours for your initial oil change. You'll have some wear on bearings and such where everything is mating together and you'll end up with a bit more heavy particles than normal. After the initial oil change I'm not for certain, maybe 250? I bet lincoln has the owners manual online where you could find out.

if you havent installed an hour meter, i would....just so you will know how many hours are on the overhaul if you decide to sell the machine....the first question asked is "how many hours is on the overhaul" i change mine every 100 hours.