OK...so I'm looking at the files, and it looks like the original digital transfer file is already fully normalized...which I think you must have done...?
That makes it a bit awkward to work with...because if/when I apply any kind of processing that boosts, it will push the total level into the red.
Now...I can still get around that by simply lowering the total level before processing, bouncing it and then normalizing it back up...but it's kinda backwards working that way.
I can also get around it another way...and just DA back out and do the processing in the analog domain with my hardware EQs...and then AD it back into the DAW.
TBH, I don't think either method will sacrifice any audio quality...just commenting on the options and something to consider in the future.
Your better off saving normalizing for the end step...after any processing/mixing is done, and that would also apply to individual tracks.
I've seen some newbs record tracks, and then immediately normalize them to "get more volume"...and most DAW will hid the truth from you, that you are no over "0" dBFS and technically clipping, because their processing is able to deal with it...but you get bitten later, when you try and bounce out to a 16bit finished file.
Also...TBH...I don't really hear a volume "drop" in the vocal after the intro...it's just how they mixed the vocal, and the backing tracks are pretty punchy, while the vocal is a bit subdued. Anyway, I think some of that will change after processing...and I don't want to try and raise the level of the vocal sections, because that also raises everything else in those sections.
I know...and you know...that ideally if you had gotten your hands on the multitrack tape, you could basically remix the whole thing...but TBH, I think the mix is quite good for that period, and it just needs a little "lift" due to tape copy and age degradation...so we don't want to try and muck with it too much.
By the way, I checked out the website for your brother...very nice, and even without seeing that, I was going to say that just based on this one song, I could see he was quite talented in both his musicianship and songwriting/arranging skills.
So...all those other songs/albums on the site...did you have to go through the same process as with this one...or were they acquired a different way, and did you have to do any work on them?
I'll get you the finished file soon, I just want to try a couple of approaches and see what works best...tomorrow you should have it.