Under normal conditions, No you wont lose power. But if ther is a tear or cut in the hose that connects the pump to the feed pipe then your screaming sound is you sucking air thru the main pump. That's not good.

Just last weekend I did my in tank pump. '89 240. I had access from the trunk. as the other guys said, clean 20 years of sand and garbage away from that crown nut, spray it down with WD-40 so it hopefully seaps under enough to help in screw it.

Use several of the crowns to loosen it if you just hit one of them, it actually makes it bind, so do a tap on one, then move to the oppisite side and give that one a tap. Same thing when reinstalling. a little Vaseline under that crown nut and use different crowns as you tighten it.

I was going to take digital pics, just in case someone asked...damn, i should have.

/// Your intank pump may be bad but given the age of your car the likely source of trouble is the 1/2 inch hose connecting the intake pump to its' output line. There is a compression fitting over the axle to disconnect the return line so you do not have to cut it to gain access. You will understand when you try to remove the gas gauge/pump assembly. The lock ring in the gas tank can be removed with a wide blade. I use a short handle garden hoe. Spray the lock ring area with WD40 to help remove the ring and to clear trash from the area. There are tests you can devise to detect that rotted hose but again given the age of the car you need to pull the pump and look at it.

No. Usually the only symptom is a fairly harsh bucking under acceleration.