Jeremy, if you have bleed the brakes properly and have a solid pedal then the first adjustment that you need to check is the free play at the top. This is adjusted by the clevis on the master cylinder and should be a little less than an inch. Then with a good firm push (50-75 lbs) on the pedal you should only have 2"-3" movement from the top. That should put you somewhere around 6"-7" from the toe board. I believe that the GM minimum is around 3 1/2" from the toe board with the floor mat in place. This distance is set by how close you have the shoes adjusted to the drums.
On the Huck brakes the leading and trailing shoe at each wheel is independently adjusted and must be adjusted in unison so they both have equal movement out to meet the drum. If you haven't properly serviced the wheel cylinders then in all likelihood you are not going to be able to make this adjustment. They are difficult to adjust even when new and you will probably need to bend a standard adjusting spoon some to fit to make the adjustments.
Denny Graham
Sandwich, IL

Denny G
Sandwich, IL