Ah! you mean the pushrod tunnel, not the cam tunnel (trough).
Yeah I did drill those drain holes in the ally barrels.
Blocking them would supply oil to such holes, but it will cause oil retention in the top end. The pushrod tunnel would fill up & it'd puddle in the back of the rocker box. Possible breathing problems and if inlet guides aren't in top condition, oil being sucked thru into the inlet tract.
Tiny holes in the faces of the followers wont allow enough drainback.
I did consider putting the holes behind the tappet block rather than in front so the oil would go into the cam trough, but there isn't really enough room.
As long as the cam trough is full of oil, which it should be most of the time, then there should be adequate lubrication.
Cam & follower wear is always a bit of a problem on A10s. The cams & followers are too soft. stellited followers and nitrided cams would fare much better, but radiused followers that cant rotate are not the best design.