Hold on to your hat boys, this thing is huge. Compared to the ECM (E38/67) on the LS3, the new generation ECM is more than double in size. To get this thing to fit, I cut off the back side of the heater and boxed it in. You have to use a big block heater system because the small block core coolant pipes exit in front of the back of the block.If you don’t want to mess with that approach, it’s best to install a Vintage Air system, throw away the old school heater core and install a blanking plate. This is what the factory did on the 1970 SEMA Camaro.
After much deliberation I decided to drill mounting holes through the thin sides and use the existing heater box mounting bolts. Add a nut union and you’re good to go.