If you can find some or borrow some, scales are the right way to finish the job. They are ~$1100 or so, and I know it is a *** of money to spend on something you'll only use once.
Regarding brake balance - if you are like me, you let off the brake when you hear or feel the first tire skidding. (Aaack - flat spots!) That means there were three other tires still rolling and capable of further braking. With poor side-to-side balance you are limiting your performance to that of the worst case tire. If you balance the fronts side-to-side, you can push on the pedal harder (duh) which will apply front brakes more, also apply rear brakes more, and by slowing down faster, throw more weight forward. With more weight forward, there is less weight on the rear, so the front-to-rear balance may be closer to about right after all.
When you put on slicks, this front weight shift increases further. The sticky tires will allow you to push harder yet, lightening the rear more. Now you're in braking nirvana, getting all four to slither simultaneously at impending lockup... ~~ shivers~~
