HEI in Mopar ECU casing

ok need some help with this. Using the 8 pin doesnt leave much room inside the empty mopar box, no way to mount the 8 pin to the box and use the mopar heatsink. SO, i am making a heatsink that will bolt to the firewall and stay there, and the HEI unit will screw to it, then the empty mopar box will cover it and use its original bolts to the firewall. Now, i have 2 pieces of aluminum i am using for a heat sink. I want to stack them and bond them together somehow so it will be one thick piece, and plus, it will let the plastic channel of the HEI unit hang over the edge so it will sit correctly..

How can i bond these 2 pieces together good and tight so heat will transfer from one to the other? Plus after bonding them, i need to drill the holes and tap them to mount the HEI unit.


2 pieces need bonded together somehow..


once bonded together, the HEI unit will mount on them like this




The heatsink will be bolted to the firewall with the HEI and the mopar box will just cover it using its original bolts


So, If i sandwiched some heatsink compound between the 2 pieces of aluminum, what can i use to bond the 2 pieces permanantly?