The 340 is out....again.....
How tight was the cam before you ran the motor? Did it spin easily by hand?
When I built my 340 in 2015 I knew the cam was tight but there wasn't much I could do about it at the time. Ran it for a while and pulled it and tore it down due to an unrelated knock. The cam had self clearanced and now it spun great in the cam bearings...which was not a good thing. The cam didn't want to come out. When I pulled the cam out, one of the bearings came out with it and it was NOT pretty. There were metal shavings clogging up the oil holes in the bearing and it wore down the cam journal as well. Luckily it didn't spin in the bore. When I had the machine shop install new cam bearings they had to hone the bore to get the new cam bearings to fit right because it was a TIGHT fit.
Oh, and it made enough shavings to trash my bearings!
Your issue could be non-related to oil if the cam was too tight to begin with. Just something to think about.
Good luck and I hope you find the issue!