My 56 build

[dsraven]

you could look for some exhaust gasket sheet and cut your own
you could look for some silicone heat resistant gasket sheet and cut your own
I would opt for the silicone sheet personally
if you find the exhaust pipe shakes around and causes rattles you could use a flex pipe somewhere close to the exit and then clamp the pipe so it doesn't move so much with engine torque etc, or you could wrap the inside of the trim pieceor outside of the pipe that sits inside there with some silicone sheet
just some thoughts, you may not even have an issue with rattling so no use what iffing it to death first. haha. I would insulate the trim part though, paint ain't cheap