Re: where did you put your harness?
On my 67 without air it was run behind the motor, thru the firewall and computer was mounted under the dash. The motor hides the hole and its nice & neat. Depending on what motor mounts you have and how close the motor is to the firewall, u may not be able to fit it there. On my 69 I ran it next to the AC lines and mounted the ECM on the inner fender. That way the hole was much smaller, as there are a lot less wires that have to go thru the firewall. Are you running stock heater box? Any pics showing how what the underhood setup looks like?
69 RS LS3/T56
68 Firebird vert LS1/4L60E
67 RS LS2/T56