Need someone to help explain this strange problem. Have factory idiot light (oil) that will cycle off/on at idle and only after I have driven the Dart at extended freeway speeds for more then a hour, does not occur at low rpm or in stop and go traffic and never overheats. Have replaced sender and wiring and checked light for possible short with nothing unusal found. Tough engines these slants! Next step is to put in a guage to see if anything is amiss with the pump.

A mechanical gauge will probably show, that you have very low oil pressure. After driving it at extended highway speeds the oil gets warmer than it does around town stop and go driving.
The problem is you probably have a bit of wear in your rod and main bearings (don't over look the cam bearings). How many miles on the motor? Lots of around town starting and restarting of the motor?

Is the pump still OEM?

-D.Idiot

Silly question. Whats your idle speed set at?

I really do, My 76 Feather Duster still had the OEM oil pump in it when I rebuilt the slant (owner said 200K+ on the OD never put in a new oil pump...that's 24 years). My 74 still had the OEM oil pump(26 years), before that slant lost it's bearings, now it has a 76 block with an OEM pump(27 years old...)....

if the previous owner wasn't good at maintaining a regular oil change and check the fluids type person, and say the second owner was a fan of the 10k oil change and slick 50 will save the day...then the rotor might be a bit worn and out of spec....

-D.Idiot

Answers to your questions: Motor last overhauled in April 1972, and then driven for 5 years before being parked until 1994 when i aquired it. Headjob done after I aquired it and four bent pushrods found along with frozen rockers. When I had head off pistons and rings looked good, very little carbon, 3 inches of sludge in oil pan found, cleaned and new gasket applied. Rods looked passable at the time no bluing found and all bearings intact although did not check clearance. Run 750 rpm at idle. I know the oil pump not to be orginal as I assisted the previous owner in its replacement and would be a stock parts house brand (this guy epitimized the word cheap, have seen him re-use used parts), believe this was done sometime in the early 80s. Still runs like a scalded cat so no complaints from that quarter although have a low mileage 225 out of a 66 that I know its history as I rebuilt it for my wifes Dart, think its time to do a motor swap, by the way my motors not orginal to the 63 as it has a 68 casting date and the prototype Earl Sheib paint job!!! Happy Slanting