You can find Steve Strange's book at his website,
www.bossperformance.com , but I think he's getting over $100 per book now for new copies.
They made 859 Boss 429's in 1969, and 499 in 1970. All are identified with a "Z" as their fifth digit in the VIN. The first 279 cars built in 1969 are the most sought-after due to their having the 820S motor, which performed essentially the same as the later 820T motor, but had really beefy NASCAR-spec internals. All motors had the car VIN's stamped in them, but swaps are certainly no problem (mechanically, anyway-as always original motor = $$$).
The 1969 cars hold an edge in value over the 1970 models in much the same way 1970 Boss 302's edge the 1969 models. It's just a public demand thing, probaly brought about by the lack of publicity on the '70's (they were old news in '70, all the magazine ink happened in '69). Cosmetically, '70's suffer a little from the hood scoop no longer being painted body color (all were black, making them look tacked-on, or Day-2-ish if you will
), and their "semi-deluxe" interiors, which had standard door panels but nice seats and dash.
Market-wise, you're looking at $50-100K, with a few killer cars breaching six figures over the last couple of years. I'd advise against a project, especially one that isn't totally complete, as due to the spreading of the front shock towers by 2" to make room, most of the stuff in front of the firewall is Boss Nine-specific, and runs in to big dollars. For example the fan and the shock tower brace can each run you $1000.
Neat cars, good luck on your search.