i need help with my 72 chevelle.first i would like to put in a newer steering coloum with tilt that would bolt right in with minor mods.second i would like to find a posi rear from a newer model year.i read somewhere that maybe a late 70 or 80`s trans am,firebird or camaro might fit.thanks any help will be appreaciated.  

No, a rear from a late 70s or 80s Trans Am will NOT fit your Chevelle (the Chevelle/Malibu/GM A-bodies are wider than the F-body cars), and is weaker than the rear in your car now.

First, what rear does your Chevelle have? 10-bolt or 12-bolt. If it's a 8.5 inch 10-bolt rear, you cna get good aftermarket parts (and a posi unit) to make this rear great for your car, depending on how much horsepower you're puttting to the rear.

If you've got a 12-bolt, upgrade the internals and stick with that, a later rear won't be near as strong.

As for the steering column, I'd check out Year One's Chevelle catalog and look at their aftermarket colulmns, or check out IDidIt.