I know its happened to me years ago BUT I forget...
if you hook the dist wires up backwards what occurs,
will you get a miss towards the higher rpm... this
is a MSD 6al box
thanks

I have heard this but I have no personal experience.

Have seen it cause different problems. The high RPM miss was the problem I saw first time I encountered the wires being crossed. Other problems were hard starting, SEVERE kick-back. Also, have seen them start OK but when the timing light was hooked up, it would show massive advance or very irratic timing. The leads on the pick-up coil should be orange&black and black with violet tracer. The wires in the harness from box to distributor should be green and violet. The violet does NOT go to the violet tracer!! The solid violet wire goes to the orange&black(+). Also, be sure to peel back the black protective sheathing on the wires coming out of the box. I have seen them crossed in the connector there too. Basically, I guess there are 4 places that they could be crossed.

If your timing seems to be jumping all over the place, check the following items:

What kind of timing light are you using? Many lights have trouble reading the MSD's capacitive discharge multiple sparks. Dial back timing lights are not recommended. Try another non-adjustable light and check the timing again. MSD offers a Timing Light, PN 8990.
Make sure you are not using Solid Core wires.
Inspect the routing of the Magnetic Pickup Harness. It should be routed clear of the coil primary wires and plug wires. It is best to route it along a ground plain such as the firewall, frame or engine block to form a shield around it, or replace the Black magnetic pickup cable with a shielded Gray cable PN 8862, which has a ground wire on one end.
Check the polarity of the magnetic pickup wires of the distributor. Reverse the connectors and check the timing again. For Analog ignitions the correct polarity is whichever orientation gives the most retarded timing. For Digital Ignitions the correct polarity is whichever orientation give the most advanced timing.
On Chevrolet engines, if the timing is retarding inspect for cam-walk. This is especially prevalent on engines with a chrome or stock type replacement timing chain cover that is actually bowing forward allowing the cam to "walk", due to thin stamping. To check this, wedge something in-between the water pump and timing chain cover to keep the camp from walking. If this corrects the timing fluctuation, replace the timing chain cover.
Worn distributor gear, inspect the distributor gear for excess wear or incorrect gear mesh if the gear is riding too high or too low on the cam gear. If correct the wear pattern should show the gear mesh in the center of the gear.

The magnetic pickup in MSD Distributors can also be checked with an Ohm meter to make sure it is within operating specifications. Once again, connect the Ohm meter's leads to the two terminals of the pickup. The resistance should be within 500 - 700 ohms. If the resistance is out of this specification, inspect the condition of the wires leading to the pickup for abrasion, shorting or opens. If the wiring is okay, the pickup is at fault.

NOTE: The Ignition will check good if the pickup is at fault. Follow the Checking for Spark procedure.

Some aftermarket vacuum canisters are adjustable through the vacuum port.On the dist!

I have some aftermarket dist(I forget what brand, it
could be a MP unit)... the colors are yellow and black
so I went with yellow as the + but on the dyno I had
a (we will call it a break up) break up or a slight
miss...It was suggested it might be the valve springs
but I have my doubts(the springs have 255# on seat
and at least 600# at .550 but thats as far as my
gauge goes)on that being the issue...it started at
about 5500 rpm and the first pull didnt show it but
each pull after that did... the timing is a bit more
than I would have expected at 38*....so thats why
I brought up this question.... I wont be able to
test this till I get the engine back into the car
and flip them both ways to see what occurs

I was 'asssuming' you had a MSD distributor with the box...the colors I gave you for the pick-up coil would not be correct in your case. I would say you have the right idea. When the motor is back in the car, try switching the wires like you said. This is a typical situation where the wires do get switched easily,,,having different type connectors that will not plug together and making connections other ways.

Reversing the wires changes where the pickup reads the reluctor. When they are correct it reads the front edge, reversed it reads the back edge. It will change your timing almost 30 degrees. (Or at least it did mine)

i have switched wires on msd,and orange box's,and i usually got a miss around 3500,and engine sounded "lazy". engines didnt sound like they wanted to go 5500 or even close...

6AL or 7AL

If you reverse the polarity on the mag pickup wires it will change the timing 40 degrees and if you change the timing it will run like crap under a load