20-40..for 5500 to 6000 RPM….I’d be putting the HV oil pump you have on! It is a big block and easy to change.
You could try too run it with an extra quart of oil with the HV pump. Really won’t matter though, we have ran a HV pump with stock pans with no trouble at all. Most of the bearing trouble we have had with big blocks is with standard pumps. I know one big block we lost a bearing on was a 72 400 with the standard pump.
Unless the HV pump also has a high pressure spring, it will not pump that much more oil than the stock pump. It depends on how much the pressure is changed. For an engine only running 40 psi it likely won’t run more than 60 lbs with the HV pump, so it hardly changes anything in terms of volume or power requirements.
For power required to drive it (equation for hydraulic Horse power HHP)
HHP = P*V/1714
So if it pumps 40 psi & 10 gph, that is .23 HHP
If the HV pump makes it to 60 psi it will add a couple gallon per minute of flow, but it isn’t enough to matter, a filter is only is ussually only rate for 12 to 15 gph.
60 PSI X 12 gph is .42 HHP
Less than 1 HHP, hardly any change in power or flow.
A stock pump with tight oil clearance and a shimmed pressure spring can require as power and pump as much or more oil than a HV pump. Some of our big blocks engine will run 100 lbs cold. You have a LONG LONG ways to go before you have to worry about drain back problems.
If your only running 40 psi max, I suggest you leave your shift points at 5K. If you want to shift higher, get a HV pump and raise the max pressure so it will live for awhile.