Nice project. That's a great airplane! I was once weathered in at a mid Pennsylvania airport and wandered into a T Hanger where a guy was working on his personal P-51. The wing Gun lockers were huge and he carried cargo/luggage in them. Said he could fly it from there to Miami in just 2 hours.
I'm worried about your aluminum bearings without sump lubrication. Two cycle engines circulate that fuel/lube mixture through the crancase. That won't be happening with a 4 cycle engine. Steel/aluminum contact is dicey at best with lots of oil around it. That won't hold up long running dry. I think you are going to need some pressurized oil to those bearing surfaces.