the upper o ring mushroom gasket must be seated into the head under pressure applied. this is why the 2 studs that the new pump sit on have hole slots on the pump itself. so you can apply upward force to the pump to pull it into the head.

i have found the easiest wayt to do this since the position is very awkward is to use a screwdriver slightly smaller diameter than the bolts that bolt the pump to the block.

take 2 of these screwdrivers (philips head) and carefully insert them in the pump holes and into the threaded block slots. carefully, u do not want to damage the threads in the block.

now with pump loosely attached to the 2 studs use the screwdriver handles now carefully to apply upward pressure on the pump to seat the mushroom gasket in the head.

make sure oyu have enough meat of the screwdriver inserted into the threaded block hole below the studs the pump is hanging on.

the slots in the pump where the studs are thru will shift upwards as the pump seats. you can feel it seat.

now carefully and swiftly tighten the nuts already loosely on the 2 studs.

this method assumes you have already applied and loosely seated the heater bypass pipe and o ring in its slot


ps. if your pump does not have 2 slotted holes where the studs ride on it is cheap model.