Since it's an old car, I'm thinking a "slim jim" might to the trick 

-Adam Wartell
NCM Lifetime Member #1222
Founder: C3 Vette Registry 
C4 Vette Registry, C6 Vette Registry

My first Vette, now owned by JB79:

Thanks Manchester, I think that's part of the problem because I've just read that there's a tension problem when you put a new door handle on. However, before I can do any of that I have get the door unlocked, so I can get to that adjustment. Thanks for the info.

Thanks Adam, that was my first idea, I made one up and it didn't do the trick. However, I've since found out that this maybe the result of incorrect installation of the new door handle. There's a different lever I need to get too, but it farther up the mechanism(almost under the door handle) and harder than stink to get to it, but I'm working on it. Thanks for the suggestion tho. Milt

Yes, correct. You need to press on the actual door lock assembly. If you have a assembly manual you can see the process and how to locate it. 

Click on image for full view

This happened to me n my 78 a year or so ago. You can get the door panel off. Youcan get to all of the screws by moving the seat back & forth.  Then pull panel out.

You should be able to get the the door latch rod and push it out of the latch to see if that is the problem.

If not then the lattch is stuck in the Locked position.

There is a tab on the inside portion of the lock that you can hit to open the latch with the window down.

It will take some force to move the lever.

I never could do it so I took it to my mechanic. He did and put in a new latch.

Don't want to be judgemental, but the handle installer should have verified all the mechanism worked before finishing the door panel installation. The connecting rod MUST insert in both points with NO tension on either points. 

Click on image for full view

Perhaps these will help with the visuals...

Joel Adams
C3VR Lifetime Member #56    
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(click for Texas-sized view!)             NCRS

"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"

Thank you Everyone, who responded to this posting and your suggestions.. Greatly appreciated!!

In the end the attached YouTube video was the answer to my issue and I was able to open the door. HOWEVER,  it wasn't as easy as the demo in the video showed. There was no way could get a long screwdriver to that lever without the inside door card being somewhat removed. Maybe it was because I have a Silver Anniversary edition (Since repainted black) or what but the guy in demo did not have a door card on that door (besides not having an outside wall (LOL)).

Having looked at the whole mechanism, I WD-40 the heck out it, and will fix what he suggested at the end of the video to stop the problem, but I think I'll treat the car to a new unit all together, but not right now. Thanks!

The video:  https://www.youtube.com/watch?v=BldEzHHDiM0

I saw that video too. I just couldn't hit the tab ard enought to make it come loose.

My mechanic oviously new how hard it had to be hit to make it release.

Hey Len, did you take it to DMS?

Of course. I wouldn't trust anyone else. LOL