ideas on SS expansion, 69 3" rear exit with ridetech

[camaro427-69]

just wanted to get some ideas from you folks on my exhaust. i had picked a flowmaster do it yourself 2.5 system due to fitment ease, that we built first, but then i decided to hack my old BBC 3"stainless system to rebuild it. the rear exit is screwed to the frame and connected to the exhaust with a 7" flex pipe to reduce drone and give the exhaust a bit place to move. but what i don´t know is how much are the pipes gonna move when things get really hot and i wanna get it right the first time. i have about half an inch space on the top 90" elbow to the ridetech frame and i run around right in the middle between coils and tank. any experienced people out there who could chime in and tell me that it is enough space.....

thanks
pat