not necessarily. The ones I had weren't feedback carbs. the only thing they didn't have was the ported nipple for a vac advance. Only Cali and hi altitude ones were feedback. My 87 Dodge van w/a 318 was the same way. No feedback. and a 318 2 barrel Carter BBD or Holley 2280 will definitely bolt directly in place of your 87, 3.9 carb. NO doubt about that.It's not really carburated; that carb is an electronic feedback carb.
You may have to find a close enough V6 distributor; the 3.9 never had any advance at all in its distributors, 1987 included in that (all done electronically.)
I'd look for that older 318 instead; it'll be easier to get running.
Might want to consider a 46RH/A518 transmission; those are basically 727s with OD and lockup torque converter, and the OD and TQ can be handled with a vacuum switch, two pressure switches, some tubing, and some wire; no need for switches or a computer of any kind.