Just did this the other day on my 39 Short. There should be seven nuts on the back side of the trim. Don't be surprised if even after soaking in blaster you wind up shearing the nut off the stud. I was successful in removing 4 of the 14. Keep the broken t-slot fasteners. I ground off the remaining threads, tapped a new hole and welded in a new section of all-thread. It took a little time, but I didn't have to hunt around looking for an alternative fastener. Also, you'll likely find a heat shield attached to two of the fasteners. Mine were rusted out, so I used them as a template and made two new ones out of sheet metal. Let me know if you have other questions.
With regard to the sight glass bolts, I'd let them soak as much as possible. When using heat, remember that the pump was manufactured in the late 40s and very likely completely coated in lead based primer.
