Any suggestions on how to either fabricate or acquire the plastic piece at the top of each door panel (the curve piece) that connects the door panel at the top and allows you to fasten the weather stripping on ether side of the window? Thanks.

 

I'm not positive,but i think i have seen a few companies selling that part.I know you can buy a complete door panel that comes with that part,so i would guess they are making it.Another option would be to watch craigslist or ebay for door panels that maybe are ripped or something but still have a good top rail.

 

Are your's gone or just in bad shape? If they're still there you can cover them with thin naugahyde in a matching color. I did that with mine that were pretty shoddy. I got some nice thin/pliable naugahyde and then used contact cement to put it on. It looks better than the stock fake grain plastic.
Here's a picture of them on my car:

 

Wow - that's looks great. No mine are still there - the driver's side is just cracked up/rotted out, but the naugahyde could save it. Thanks.

 

You can buy the material at Fabric Depot cheap! I paid about $5 a yd. on sale for 60" widths. You can also pull your's off and glue them together on the back side to hide the cracks, then use some plastic filler to fill any surface issues before covering.