Most of the Monte Carlo bucket seats I have seen and had did not have the "bullet" end caps. That being said, my 70, "Big Red" has them now. Without the end caps, to me, looks unfinished.
After removing the rear seat and side panel you will need to unbolt the window regulator from the body of the car. Then see if you have enough movement to take the regulator off of the window. If not you may have to loosen the window stop (on the bottom) and possibly remove the window track itself to gain the room .
I did the same thing to "Barn Find", my 71 402 Monte that was off the road for over 34 years. Check out the thread" awake after 34 yr slumber.
With the exhaust manifolds off it's easier to r/r the engine mounts. I used a ex and a floor jack under the sump of the oil pan. Do one side at a time. Should go smoothly.
Well, it's a 70 Flint built car. Meaning, NO build sheet. The last 6 of the vin seems to be early in the production run, so it may be possible the story is correct.
Both work on each other. Usually though the big block and high performance small blocks had the "canister" type pumps. The lower body of the pump is bigger.
What is done to your 454 and what is it doing that you feel it's pump related?