Realistically, I think it's going to come down to finding the bullet (and powder) combination that this particular barrel prefers. I struggle to make an L42a1 consistently a sub MOA rifle, but sometimes they do a five or ten shot group around 3/4 MOA. The next time out, there will be the start of a screaming 1/2 MOA group, and then one or two will "leak out", making a 1 or 1 1/2 MOA group. (On the rare occaisions that I'm doing "serious" bench work, at any rate...)
Sooo....If you can get a .303" combo to do consistant 1 to 1 1/2 MOA groups, DON'T change a thing! Anything under 2 MOA ain't bad.
Sounds like fun finding out, though! I LIKE "sleepers".