Yeah, that was mine. Every 12", but closer at the piston location. Worked great. Buy Stainlesss Steel rivets, (1/8" x 1/4") as they have twice the tensile strength of the steel rivets. Since you're buying a gun, get the kind with a swivel head, it'll be handy for this app. Very narrow area where sheetmetal is located under the plastic lips of the OEM portion. Look at it carefully to center the rivets well, vertically.
I have a welding background, never got to see Thermite, but am familiar with it of course. Thanks for the reply.

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Majestic Blue 2006 XE CC 2WD Big Tow
AEM BruteForce CAI; PowerAid TBS; MagnaFlow 3" x 24" Muffler; UpRev 93 Tuned; Detroit TrueTrac
Stillen Front and Rear AntiSway Bars, Diff. Cover, Front Rotors & Pads
PRG 2-1/2" and 1" MiniLift, Street Traction Bars
DYNO: 308 RWHP & 380 RWTQ
~CRANK: 360 HP & 450 TQ
Born June 12, 2006
Adopted June 27, 2006
14.792 secs at 91.04 mph prior to TrueTrac
Member of the Charm City TitansIRC VK56 Member "Special Operations"