i sorted this problem i had when i fitted a oil cooler from a mazda rotary in place of the airbox - it takes an extra liter of oil which meant i now had a liter less
took an old sump , cut out the lower middle piece ,cut and welded it into my sump .added a piece of tube same length as the added piece to the pickup.i now have an extra 1.5 liters.
the more oil , the less chance of surge?