I just took the chambered system off of the '68 Z-11 I bought earlier this year due to the rattling. I took the system down twice and tried to adjust it but nothing worked. The Z-11 (convertible) is a 350, not a BB.
I have a chambered system on my Z-10 (hardtop, 350) and that fits fine, no rattles or problems.
A good friend (KevinW) of mine put a Ricks standard 2" on his '69 convertible and most of the system was fine with the exception of the angle and length of tail pipes. We did this on my lift so I was ther to help.
While this does not answer your direct question, I hope this helps.
'68 el Camino SS 396/325 hp, 4 Spd, 3.31, Buckets, AC
'72 el Camino SS, 454 LS5, 4 Spd, 3.73 LSD, Buckets, AC
'75 el Camino SS, 400 SB, Turbo 350, AC, Swivel Buckets, PW, PDL
'87 el Camino Choo Choo SS (305 TPI, 200R4, 3.73 LSD)
'87 Buick GN Hardtop