hi

got one of the mopar /mallory adjustable distributors with a collar to limit play .

set timing at 34 at 3000 and it drops to 26 by 4000 rpm ????

vac disconnected

crome box big accel coil 1.25 resisstor

ideas entertained !

thank you !

The chrome box is probably bad. Try a different box.

I've seen that when a low deck BB distributor was used in a SB LA motor, all BB distributors are intended to rotate counter clockwise and all LA SB and early Mopar V8 with the distributors in the rear rotate clockwise
I've also seen what Andy is saying on after market ECU

I have a YH mallory and it does the same thing. It hits 38 degrees at 3000 RPM then drops to 35. My understanding is as the weights hit the limiter they retard as the vibrational forces cause them to bounce.
If you look at the original Mopar Performance Distributors they place a very strong spring with a long loop with a very light spring so as the advance rises rapidly and then the slack is taken up and then the heavy spring begins to limit the advance to a slower rate. There is slew rate but i don't think that is the issue here.

What springs are you using? You could try a light spring and a heavy spring