Neither of those bikes will bring you much joy for extended highway driving.
The 350 is just not enough motor, the 500T is a step down from the original 450.
I love my 450 above all bikes, but it will buzz you to death on the highway, even geared up like I have it.
Though I've gone coast to coast a number of times on 450's, I was young then, and tough. I couldn't deal with it now.
Find yourself a nice Gold Wing somewhere - in motion they handle much better than you'd expect, and can sustain comfortable highway speeds indefinitely, with tremendous rider comfort. And they're plenty fast, don't believe anyone who tells you differently.
I rue the day I sold my 81 Naked Wing, I must have been insane (actually I was broke, had no choice).
But to answer your question, the 450/500T parts do interchange, in this case.......