yes there is a difference, 78 and previous required a gasket ffor the Pinto and is smaller than the 79 and 80 that was a glue in type

Brian is pretty much correct, but in the middle of 1978 they started using the glue in smaller windshields

middle of 78 is when the 79's were being built at the assembley plants. when asking "glass guys" for a windshield for a 1978 Pinto they (glass guys) refer to build date and here's where it gets confusing. there are only 2 different windshields for the Pinto and 79 and 80 is larger than previous years because the gasket wasn't used.

I would "guess" since the question of a replacement windshield for a non-pinto kit/replica and if a gasket was used previously it would be the early windshield that is needed since the later (79-80) is bigger than the early one. Would be nice to know what "replica" this is for, with that info I am sure there is someplace to find the correct answer on what will fit this particular application even if the company building them is no longer in business

I learned the hard way... tried to order a 78 windshield for one of mine... it was a confusing mess for the glass shop till I figured it out and had to explain it to the gal he had working for him ordering glass. In the end I'm not sure she understood and think I just told her to order for a 77

Karma kit ferrari dino 246

it uses a rubber, i would bet heavily on the early model since glued glass and fiberglass bodies will blow up windows plus they probably used an off the shelf gasket which the later glass doesn't have available.

OhSix'

when it comes to rubber go with steele rubber products!!!
 
 

A bit further east, Hawick in the Scottish Borders, I think we share the name and the weather!

I suspect you are right about the opening size being the same.  One problem is with the interior trim.  In early models the rubber gasket provided a finished appearance to the interior and held in the head liner.  The windshield glue in models had an extra small strip of metal welded to the interior of windshield opening flange.  This strip of metal holds a plastic trim piece which provides an interior finished appearance and covers up the edge of the head liner glue joint.  Not sure if the rubber gasket would fit properly over the window flange with this extra strip of metal there.  Maybe the extra strip of metal could be flattened or removed.

Not having tried this, there may be other difficulties and solutions.