sharp, as the "TT" guy, we've chatted motorcycle stuff in the past, so you'll get this. As another old motorcyclist-this makes me think immediately of how Ive always had and preferred a more medium "sport bike" position , and even 35 years ago I used to look at Harleys and whatnot with the high bars and forward pegs and all I could think of was how it would put weight and pressure on the lower spine and keester.
Seat density and shape, but especially that balance of peg, bars position to counter wind on our body is key to long hours riding.
With bicycles, no wind support, but leg support while we ride, yet the same seat-bar-pedals relation ends up being similar, finding that right balance doesnt it?

as mentioned, you might be able to counter stuff to an extent. Be careful though of forward seat position, just check to make sure your feet arent tooo far forward of the pedals, not good for the knees, but you should be able to gain an inch or even more without problems.
You can always go for a longer stem also (a pain in the arse I know with trekking bars, have to remove tape and everything) , getting the bars ahead a bit along with seat can help.
Shorter cranks also could help, but then thats an expense not worth doing.

try mucking about with the seat and bars, start with seat and see if it gets you forward enough, then look at stem. Although I know older type stems arent available that much, you might have to try one of those adapter thingees that is just threaded "pole" with the expander thingee, then you add on a regular stem to it.
Used bike places always have a box full of older quill stems for 5 bucks or whatever.

oh, make some detailed measurements from your old bike to try to copy with your changes, being logical with what you measure.

worth a bit of trying anyway.
good luck