Just so you have the background, here's the overall sequence:
PM-1 through PM-5
Chalkdust Basic Math 6 (skipped chapters 6 & 7 on business applications and statistics/probability) -- started this in the middle of 6th grade
PM-6 (but faster than the earlier levels of PM, using less IP & CWP)
NEM-1 (first several chapters; none of the geometry chapters)
Chalkdust Pre-algebra (textbook only), selected portions
For CD Basic Math 6, I have the complete set with DVDs. But for the CD pre-algebra, I only have the older hardcover textbook.
There's some overlap in content between CD BM-6 and CD Pre-alg, which I wanted to skip. So we focused on doing the new stuff...stuff with integers (negative numbers), solving equations (wherever there's a variable), and exponents.
We did something like this (CD Pre-algebra, 2nd edition):
In Chapter 1 Whole Numbers, we skipped everything except "solving equations with whole numbers" and problems with variables. We did all of Chapter 2, Integers. In Chapters 3 and 4, Fractions and Decimals, we just did the problems with negative numbers and/or variables. We did all of Chapter 5, Variable Expressions and Chapter 6, First-Degree Equations. For Chapter 7, Measurement and Proportion, we did it the same as we did Chapters 3 and 4. I don't think we even got to Chapter 8, Percent! And we skipped the geometry chapter and the statistics/probability chapter because we ran out of time.
We kind of had to fly through the CD Pre-algebra text, picking out only the new stuff to do, because we didn't start it til nearly the end of ds's 7th grade year, maybe the end of April or beginning of May. And he was getting ready to take the admissions test in June to go to school for 8th grade. It worked out fine, but you may want to include more review.
HTH!