With FTsolid cams I run it for about 45 min with only the outer springs @ 2500+ rpm.( Your Roller wont need that) Then fit inners and run for about 2 to 3 hours before changing
oil to race or performance type. Rings should be 'bedded in' within the 45 minute time. Try to avoid any high loads during that 45 min if running in the car.
I take it that you have looked at the 'Low Profile Flowmasters' ( 2.5" thick), same pipe area as 3.5" tube.
Jac Mac