What year is your car. The early A bodies have tight engine compartment but it is still possible to remove the oil pump with the engine in the car.
Worst case you will need to loosen the passenger side motor mount, then use a jack to raise that side of the engine to get the pump out. You will be able to reach the bolts, but will need the clearance to extract the pump.
Don’t be surprised if your OE pump has six mounting bolts and the replacement has five. The five bolt pumps seal up fine. Also look at the photo of the pump in the ad. Does it come with the drive gear installed? If not get one with the drive gear installed. Moving the drive gear from the old pump to the new pump is doable,, I have done that many times, and can walk you through it, it is just one more thing for you to deal with.
With that said, I would mount the mechanical oil pressure gauge first and verify what the oil pressure is before changing out the pump. If you do have an oil pressure issue, it could be the oil pump bypass is stuck open,, to fix that right you will still need to remove the pump from the engine, but you don’t need to spend 80.00 on a new pump. If you do the standard volume is fine.
