I just did a quick search in the service manual and it looks like a pretty in-depth project. I picked up the service manual on disk on ebay. I could try to help out so send me a PM with your email or fax number. Good luck.
PS - how did you narrow it down to the oil pump?
OIL PRESSURE DROP
1. Low oil level. 1. Check oil level and fill if necessary.
2. Faulty oil pressure sending unit. 2. Replace sending unit.
3. Clogged oil filter. 3. Install new oil filter.
4. Worn oil pump. 4. Replace worn gears or oil pump assembly.
5. Thin or diluted oil. 5. Change oil to correct viscosity.
6. Excessive bearing clearance. 6. Measure bearings for correct clearance.
7. Oil pump relief valve stuck. 7. Remove relief valve. Inspect valve and spring. Replace as necessary.
8. Oil pump pick up tube restricted,cracked, or damaged. 8. Remove oil pan and inspect oil pump pick up tube. Clean or replace as necessary.
9. Oil pump cover loose, warped, or cracked. 9. Inspect/tighten cover screws or install new oil pump, if necessary.