Are these pieces on the inside of the doorway matching up with baseboard tile? What is on the wall exterior of the door? Is it baseboard or tile baseboard where the grout line can match up to the upper edge of baseboard or grout line tile on walls. Not sure I explained myself well.

There will be a glass door that rests on a solid marble threshold. The tile guy is using thresholds on the inner edges of the shower entrance. Is that what you meant?

I think my question is--do you mean the height is 80 inches, or the length is 80 inches? (are we talking along the bottom/front and therefore part of the pan, or are we strictly talking door jam, the vertical sides?)

I'm 6'4". But even so, I don't think a 6'6" entry would be a lack of headroom issue.

Would dropping the entry height mess with the tile layout inside the shower?

Or would raising the curb 2" have a negative effect?

Another option, but again it depends on your style of shower entry and how it's being trimmed out...

But I'll toss it out anyway:

To keep your 78" piece intact, consider adding a 2" tall "plinth block" under the 78" jamb. The plinth could be a true plinth, standing proud of the upper jamb. Or it could be flush, the same thickness as the upper jamb. The thickness of the 2" tall jamb plinth would have to relate to the width of the casing plinth.

Plinth blocks are usually used on the casing and not the jamb. But we're going with the flow here. ; )

Regardless of the plinth thickness, to do that I'd want the top of that 2" tall jamb plinth to match the top of a plinth block on the door casing. That way the grout lines look like they belong.

Since a picture is worth a thousand words...and thanks to a new scanner I got last night...

I don't know what your overall style is, but in my eye, adding a 2" block under your 78" jamb looks perfectly fine if the top edge of the "jamb plinth" matches the top edge of the casing plinth.

There are myriad variables to the above. It's a matter of tailoring it to your style and it not impinging on a door if a door will be installed.