I once rebuilt a small block ford 302. I noticed the front main bearing seemed to be worn more than the others. It fired on 1 then 5. So 2 cylinders loading the front bearing first.
( firing order 1 5 4 2 6 3 7 8 )
I changed with firing order with a 351w cam. ( 1 3 7 2 6 5 4 8