We're having a 'chat' I see! (not for long, my time is nearly up here in Tremp Library!)
The packhorse bridge is indeed unsuitable, it's not actually part of the modern route - see it here: E 342797.90338223, N 4725396.4740025 (ED50 UTM 31N)
Longitud: 01° 04' 50.4" Latitud: 42° 39' 47.3" (ETRS89 Geodèsiques)
I think bivouack should be OK though - as long as it is
bivouak. There's a refuge at Fornet just about where the Parc Natural starts (here: E 345131.90338223, N 4732302.2658161 (ED50 UTM 31N)
Longitud: 01° 06' 26.1" Latitud: 42° 43' 32.7" (ETRS89 Geodèsiques)) and I think the 'normal' rules discussed elsewhere
would apply. Camping is prohiobited in the National
parks - an important distinction - - but I'll try to find out!
Cheers - over and out for now!