OK, maybe they are related (very loosely) by being about Mopars.

(1) I have heard of using 73 & up doors on an early (67-69) Dart to eliminate the vent window. After removing the door vent window assemblies on a 68 Dart it looks like a 73 & up door glass might fit. Is it possible to use the existing door & window lifting mechanism of the 68 with a piece of 73 up glass?

(2) Can a 71 Cuda grill be fitted into a 70 Challenger or vice versa using existing mounting points?

Told you these were weird. Too much chocolate today.

Answer to #1 is no.

They had vent windows all the way through 76.

Duster, demon and dart sport had no vent windows, but had curved glass. That may be the confusion.

That would be incorrect.

My 73 Scamp does not have vent windows. The 4 door cars may have still had vent windows though.

Sorry, forgot about the Dusters ect.

My 73 swinger has no vent windows.
FYI, 73 is unique glass if i remember right. I parted a 74 and found the glass is different as is the regulator. Not sure why the change.
Im building my 73 to look like a 72. The door glass will be the only dead giveaway to someone who knows darts.

I your doing it that way be sure to use the 73 trim for underneath the roof rail trim to allow the 73 window gaskets to be used.

Sorry I wasn't clear about the possibility of using Scamp glass but the answer seems pretty well sorted - to use the 73 glass, you need the 73 doors. Thanks all!