[QUOTE=Steel isn't heat treated.[/QUOTE]
Originally Posted by powers2b
An 80's era Trek most certainly isn't heat treated. But today's high end steel alloys are heat treated. And it is indeed best to check the actual material than to guess.
And not all aluminum is heat treated. (most 6061 is, most if not all 7005 isn't) Blanket generalizations are rarely accurate!
Denting the chain stay will compromise the lateral rigidity of the frame, but how much is anyone's guess. Given the age of the frame, I'd not worry about it. Although it would be BEST to find a solution that eliminates the need to dent the frame, it would be a nice pet project. You may have some alignment issues after denting, but a string run from the dropouts past the seat tube and around opposite sides of the head tube is an excellent alignment guage. 80's era frames are absurdly easy to align compared with, say, a steel frame made with True Temper OX Platinum.
Remember Cannondale's old ads with a guy contemplating the advantages of Al while crouching on the rear triangle of a bare CDale frame? You couldn't do that with steel back then. But today you can! Today's steel is amazing!!!