[MrPbody]

Mischa, don't make the mistake of buying the crap about "you can't make a Pontiac run, you MUST use a Chevy". If you do, in a car as heavy as that Tempest, you'll get your doors handed to you nearly every time you run against a similar car with either BBC or a Pontiac (400 or bigger). This is especially true with streetable cars.
Or are you considering a 350 Pontiac? I recommend against it, as it does not respond to high performance modifications as well as the 350 Chevy, or the 400 Pontiac. Internal geometry is completely different. A 350 Pontiac is NOT the same as a 350 Chevy (or Buick, OR Olds..).
A '69 350 Chevy was available anywhere from 220 (2-bbl) horsepower to 370. These are "gross" numbers, not to be confused with the later rating of "net" numbers. Rule of thumb is to multiply "net" numbers by 1.2 to get "gross" numbers. Of course, you can go the other direction, too. An '82 350 Chevy is useless as delivered, from a performance point of view. The heads, cam and induction MUST be modified to gain anything from it.
The '71 model year is the "line in the sand" for performance engines, with only a couple of notable exceptions, until the late '90s when LS-1 came around. That was the year ('71) when the government mandate for use of "regular" fuel was implemented. The result was horsepower falling off the table for years to come.
The 440 question is valid, but there's an important point missed. The earlier 440s with higher compression and more aggressive cams, were for high performance, period. The later (and earlier low compression) version is for trucks and full-sized cars. The power output and RPM range are aimed at a completely different purpose. Don't confuse power for trucks with power for hot rods...