Jmac
the description you gave of how your 86 was running is almost a mirror of how my 83, 350 was running except it was the number 5 cylinder on mine that was not firing and all gunked up.
I replaced the 350 with a 383 and a edelbrock and I have the same detent problems that your having.
never could get it dialed in. (hand shift)
the tranny was weak anyway and now getting weaker.
what I'm going to do is trash that *^%$ 700r and build a good strong 400,
screw the mileage.
T