The center insert is made of mild steel . even tho I JB welded the insert in it still bends like cheese unless I grease in every landing .They should make the whole strut slip into a socket .Back to the exhaust topic- To Create muffler pressure I drilled onlyone smallhole around 1/8" into the channel behind each exhaust stack after which the plate with stacks is pop riveted and jb welded into place .The channel is roughly 1"x1" and then lay out the elbows along side it to figure how much length you need .You'll figure it out. I mounted the manifold through the front of the firewall , I basically made a hole about twice the size of themanifold end with some of the plywood firewall flanging out on one side to mount the unit. this also allows for cooling air to get in which then exits out around the stacks .If Iever have the cowl off again I'll try to remember to take some pics