Robert, let me ask you again what is your end goal. And before you can answer that, we should discuss what you are exactly doing. For example...
Are you running solid or hydraulic lifters?
Are you pushrod oiling?
How many RPM will the engine run?
What type of oil pan can you use?
Answering those questions should direct you to what modifications you need to make, if any.
Now lets play the the game. Keep in mind I'm assuming you have full groove mains, a HV pump and your pick up is well sorted out, or at least as good as you can do within the limits of the oil pan.
Hydraulic lifters? You are screwed. All you SHOULD do is tube the block, drill an .080 hole in the tube where it breaks through the lifter bore. For the passenger side use a set screw under the main bearing to restrict flow to the drivers side.
Solid lifters? Much better. Tube the block. Block the feed to the drivers side as above and go.
Pushrod oiling? Now its more work. Tube the block and drill the holes for lifter feed in the tube. Use a plug under the main bearing with about a hole in it to feed the lifters.
How many RPM? If you are under 7500 then worry about the inlet side of the pump and getting the pan in shape to go around corners. If you are going much higher than 7500 you need to address the elephant in the fridge and that's getting the oil to the rods. I'm not addressing that here.
What pan? Mid sump, rear sump, box style? The worst pan by far is a box pan, but I haven't done a wet sump circle track engine since the late 90's so I don't remember what you can do with a pan like that. I don't think I've ever seen what I call a box pan.
A mid sump is the second best option as far as oil control goes. Oil control is less problematic than a box pan, but the pickup tube will be longer than a rear sump and therefore as the length gets longer the cross section MUST get bigger and that's hard to do. As I said before, the biggest gains in increasing bearing life is a HV pump, full groove bearings, getting the suction side of the pump as big and short as possible and stopping the leaks at the lifter.
If you can use a rear sump pan, jump on that. Best oil control, shortest pick up tube and you can install the pick up in the cover and you can also if its done correctly will let you add a second pick up using the OE hole in the side of the pump. As engine speed goes up, getting the suction side of the pump as unrestricted as you can gets more critical.
To that end, your engine builder shouldn't be using 1970's and 1980's bearing clearances. .0025 on the rod and mains is the loosest I would use, and even at that I would spend money on a quality synthetic oil (not group III oil because its not really a true synthetic oil) because using a 20/50 oil makes it more difficult to get the oil into the pump. Or a single grade oil. Other than my compressor and the brake on my dyno I can't think of a reason to ever use a single grade oil.
Notice I didn't say use a crossover? But let's go there.
Lets say you are pushrod oiling and running right at 7500. Here's what you could do. Tube the block, put your holes in the tube to feed the lifters, plug the feed to the number 1 main at the front of the passenger side feed hole then install the crossover tube to feed the drivers side and put to the drivers side and let it get the oil to those lifters that way. That
s what the crossover does. It doesn't slow the oil down, it doesn't do anything other than get oil to the drivers side lifters. Bearing life is increased because you stopped the leaks and forced the oil to the mains rather than letting the oil leak all over the place.
Or, you could leave the crossover out and and rather than blocking the oil to the number 1 main at the front of the driver side gallery you block it under the main bearing of number 1. Then you can pick up the oil to feed the D side lifters by drilling and tapping a hole in the rear china wall where the pressure gauge feed goes up and take the oil from there to feed the lifters from that. That way it doesn't take oil off the main gallery.
If you are running a roller cam that has a groove around the 2 and 4 bearings then I would either install a set screw in the head where the oil gets to the shaft. For roller rockers a .0625 hole is plenty big. If you are running bushed rockers or any rocker that doesn't have needle bearings on the shaft you need to make the hole .080 or so.
If the engine is apart, you can clock the 2 and 4 cam bearings so you block the hole feeding the passage in the block so no oil gets through the cam to the heads. Then do the above modifications and rather than the crossover just feed the rockers by accessing the same oil gallery that feeds the pressure gauge. Then drill and tap the gallery that goes from the cam to the head that normally feeds the head and run a hose from the pressure gauge gallery to feed the rockers.
In post 4 you said you wanted to do the crossover to keep the bearings alive. It doesn't do that. All it does is allow you to feed the drivers side lifter IF you are running hydraulic lifters or pushrod oiling. Or both.
If you need to do that then you can do it, but there are better ways to do it than that. The biggest bearing savers are a HV pump, full grove mains and blocking the oil off to the lifters. And of course to get the pick up as big and short as you can.
