The 1987 3.9 had a carb. I had one and though there was no change in ratings to the TBI engine, the 1988 I bought to replace the 1987 felt much stronger.
Besides the carb, you will also have to address the ignition as the TBI surely provides feedback to the ignition. And the electronic ignition conversion kit for the 3.9 is long gone.
Besides the carb, you will also have to address the ignition as the TBI surely provides feedback to the ignition. And the electronic ignition conversion kit for the 3.9 is long gone.