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.
As I remember, Mopar Perf did offer a vac advance distributor, headers, a 4 bbl intake, and a couple of cams for that engine at one time. the long block was the same from 87-91 on the early 3.9s.
I think either COMP or maybe it was Schnieder, offered 1 step and 2 step above stock cams for that original 3.9 too you might talk to Ken at Oregon cams about regrinding your original cam into something special. You'd definitely need new lifters with a new or reground cam. Easy, as they were same lifters as a 318.
. For that matter, other than having 2 extra holes on account of being a V8, the block deck height and such is the same as a 318 so a 318 dist will physically fit into a 3.9 like it was made for it. The question then becomes if a 3.9 cap will fit a 318 dist housing...... and no, an old slant 6 cap wont work because of the 3.9's "odd fire" design. It would have to be a cap designed for a 3.9..... there is more space between dist towers on a 6 cyl cap than there is on a V8 cap.... You'd need a reluctor under the rotor made for a 3.9 (again odd fire design) Then, if an 87 3.9 cap would fit on a 318 dist body youre home free..... I think it might, considering (again if I remember right) a v6 and v8 take the same rotor.....
you might have to do some custom fabrication/machining to build your own..... tuning and such (vacuum advance, mechanical advance) would then be just like building a custom advance curve for an old 340!!!!!!
