If the security light is on, it sounds as though there is an issue with the PATS (passive anti-theft system).
There is not just one module controlling this circuit. The system includes PCM, Central Junction box, and the Transceiver. Were any of these things changed when you changed the engine size?
If so, PATS security access must be granted to erase ignition keys, enable/disable unlimited key mode, and enable/disable the spare key programming switch. It will require a scanner that can communicate with the PATS circuit. This isn't something that can be bypassed.
If you look at the pics below, they provide the directions specific to the procedure. Take a look through them and let me know if you have questions.
See pics below.
Images (Click to enlarge)
Tuesday, October 12th, 2021 AT 7:50 PM