The only info I could find (not sure how accurate) was that the 84 was stock
w/ 92 HP and the 88 was stock w/ 98 HP. Both had the same motor,
displacement bore and stroke so I'm not sure if the aspiration was changed
but the difference is only 6HP if that is correct. I don't know that a
distributor change would net 6HP but based on the info I don't think it
could hurt.  Hope that helps

Thanx for the answers.  I was curious if the the swap out was worth
the effort as the mounting and plumbing would be about the same.   6
HP spread is  not my idea of a better engine, especially if I have to
change out the associated wiring and computer.   I would like to hear
about any other GM 4 cyl that would make for a good swap.  HP at least
25% increase and decent mileage.

Pete

A different ignition system would not result in any real HP change, the
'power' required to turn the distributor is nil. Change was probably made
for reliability or because of a cheaper
to produce design. Since other cars used the Iron Duke, it was easier to
just change them all
at the same time.

The later engine from what I've read is a more reliable engine, and if your
car's engine needs replaced, for what ever reason, I'd seriously consider
putting in the newer style.