Oil pressure drop under hard braking

This is a weird one...

My Dart's engine is a '74 225 with the original 170's pan and pickup. When I installed that pan, I modified the dipstick tube of the new engine to make sense with my new pan, and whenever I change the oil, it's spot on the full mark.

When I have to stop quickly, my mechanical oil pressure gauge (and the electric one before that) drops quickly, so I'm obviously uncovering the pickup under hard braking. I installed the pickup according to the shop manual and verified it with my borescope, so I don't think that's a problem. It seems to have the correct amount of oil in the sump.

I guess I'm not sure what to do...It's not like I'm stopping that hard; it has 9" drums on it. Should I add a half quart? Is this a slant six shortcoming?

I don't think it's going to hurt anything considering how infrequently I have to slam on the brakes, but every once in awhile it happens.