I had an 8 on my very front main (5 on the crank and 3 on the block). With some research I came to believe that the later engines had an oversize bearing on the front to aid in reliability. I found a chart somewhere that gave some selections (didn't have an 8) but with some effort and some relatively expensive tools (bore gauge and mic) I determined that the bearing was within specs. I did replace all of the other bearings on the crank and am using a TT oil pump and the pressure is really good. Apparently there exists aftermarket replacement bearing if needed. I also found that you could possible shim the bearing with some regular aluminum foil on the half that does not have the oil holes.
