Hi!

well what i do when i repair an exaust is i lower the area where i want to add the carbon  so i sand the surface and cut it with a sharp knife usually i prefer square cut   , 1st i use a polyurathane foam from the stores and to tell you the truth i buy the cheapest ( all r same) i put some in the hole that was cut and  leave it for the second day , what will happen is that the foam will make u a surface and then flatten it by cutting the excess and sanding it a little lower  ,(at the same thickness of the carbon layer plus the resin).

i take a larger part than it needs and i clear coat it a little or i use a wide scotch tape on a layer so i can get a perfect cut and  i cut it with the scisor to perfectly match the area im going to put it in(weave will line up on all 4 sides) , then i use the overlay method , adding a black resin to the area covering the outside area with paper tape so it wont be touched and then stick the part i cut when its tacky , and i put 2 to 3 layers of resin and sand it to 2000 and polish it which i recommend to your part or clear coat all the part .

hope this is useful to u or at least ,may some of it give you a better idea to be done .  

best regards mhd alghoul mhdghoul@hotmail.com youtube channel :atmospherejo link is http://www.youtube.com/user/atmospherejo?ob=0&feature=results_main

tanks;

but I tink I will disassembly the whole thing and start working from the inside. After renforcing the inside, i will do was U said in the outside but without the foam,... theres a big crack that isn't visible on the picture....