I wouldn't worry too much about a few grooves in the bearing surface like that. I had a crankshaft resurfaced and ground .020 under on one journal and it still had some pits. Gentleman that did it is about 20 years older than dirt and had enough tools and experience to hand build his own engine from billet. I asked him about the grooves left in the journal and he looked at me and said "Do they stick out?" I said "No?" He said "Then it'll just be another spot to hold oil..." he kinda shrugged when he said that and moved on. This was on a much higher tolerance diesel, small engines like this Onan are far more forgiving.