Following the mantra "2 steps forward, 1 step back", I went ahead and pulled the dash AND heater back out of 1010 today to re-address some upholstery issues which I'll post separately. Anyway, that exposed my original heater hose solution (see below) that is visually hidden when things are assembled. Functionally this solution is probably OK - a mix of Pep Boys 1/2" hose bits with some aluminum tube - but it could certainly be cleaner and fit better too.
Presumably the original hose would have been European 12mm vice 1/2", since that's the size of both the central tubes & the heater core. Any pics or original parts out there?!
My car came with a mess of disintegrating hose parts, cobbled together in the worst way; no way it left the factory like that. 1/2" silicone hose might be worth a try, especially some long-ish elbows cut to length, if available. Appreciate any thoughts re this ningling issue! Nate