So I installed a new system from Classic auto air in my 69 B Body. Upon pulling a vacuum we found a leak. The leak happened to be where a screw from the firewall cover plate entered the suction line. Big props to CAA for covering my mistake under warranty. My question is do I need to replace the drier before charging the system?

Not on a brand new system. Drier will only need replacing if the system is open for a long while.

What's a long while? It's been several days

Many driers have a sight glass. I believe the normal color is blue, if it is pinkish or white then replace it. At first I thought the drier that came in my CAA system did not have a sight glass. Upon closer inspection I found it was hidden by a black sticker/painted tape (maybe to cover the glass when painting the drier?)
Anyway, if you have a sight glass and it is blue, I would say you are ok.

I found this pic online for an example.

I don't think several days will hurt anything. I was thinking weeks with a wide open system .In damp conditions.

While we are on the subject,
I am putting a perfect fit Classic AC in my 70 challenger also. The evaporator in the dash is the only component that is not being replaced.
The AC has been out of the car for several years. What do I have to do to flush the evaporator to use it with these new components? The evaporator has been open to the air for many years.
Thanks

Before filling an A/C system you need to pull a vacuum. This serves two purposes: It removes all of the air, and it also boils all of the water out of the system (you never get it all out).

Old timer a/c guy we used at 63436 would let the vacuum pump run all night, then watch the gauges ... we didn't have a lot of a/c stuff in Vermont back then ...

You just need to vacuum it longer, and make sure it holds the vacuum.
Any moisture will boil off and get sucked out of the system when you pull a vacuum on it.
At 29.02" of vacuum, water boils at 76-degrees F.
At 29.87" of vacuum, water boils at 6-degrees F.
If you vacuum the system on a warm day you should have no problem removing all the moisture in the system.

Thanks for the replies and as usual this site is full of good info.

When I converted mine to 134a using a Bouchillon kit, he told me to clean it with brake clean. That is what I did. In retrospect I should have flushed it. I now have a flush tank ($50) and a quart of flushing solvent is around $10. A quart should be enough to clean the evap.