My 451 is apart for a quick hone. Looking at the main feed holes its about 3/8" at the bearing saddle then quickly steps to 1/4" all the way to the cam bearings. Is that OK or should I drill them all out? Running a HV pump. Cam is a solid roller. Full groove mains.

This may help:
http://www.bigblockdart.com/forum/showthread.php?2118-440-block-pics-and-drilling

Unfortunately the pics are all gone, since the thread is years old, but the info is still there.

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The reason it is drilled larger at the saddle is there is an intersect point from the true main galley feed for the mains, to the cam bearing feed. The holes to the cam bearings don't need to be as large as they are, so there is absolutely no reason to open them up. In fact, making them larger would only tempt fate with as narrow as the webbing gets between the main bulkhead and the cam. Think of it this way... any oil going through those drillings up to the cam is robbed from the crank and rods. The cam needs minimal oil supply on it's journals.
There is a simple modification you can do to supply the heads with oil without starving the mains/rods. You turn the 4th cam bearing to block the holes that lead through the valley into the cylinder heads. Then drill through the valley drilling into the main lifter galleys for an oil supply.

Not only do I not drill them, I restrict them down to just lube the cam bearing (probably could be blocked with the splash, but I never went there) and take the cylinder head oiling off of the cam bearing(s).

After rereading it I thought the bearings were
small.. not the case here..as Trends said there
is 2 holes in the mains.. leave them alone... my
error

keep a steady non wavering grip on the drill to keep from tilting it & breaking the bit in two with half of it already down in there. Go at the right speed (not too slow & definitely not too fast). Have a helper constantly oil the bit. At the very end when it starts to grab as it wants to break thru to the gallery, just tap tap tap easy to get it to break thru cleanly. Wouldn't hurt to deburr the horizontle gallery when done.

How do the rods and main bearings looking?
If they are good don't fix what ain't broken
Lots of misinformation out there about oiling issues on B and RB block in the main oil galley feeds to the main bearings, full groove main bearings, good supply of oil and the proper(001+ for each inch of journal diameter), NOT TIGHT bearing clearances have worked for me for years and years
Thin oil, high volume oil pumps with 80 lbs. bypass springs in the high volume pumps and adequate bearing clearances are the key to making these motors live up to 7500 RPM

That's great. I'm going to leave it be. No need to screw up a good block. Thanks guys.