I hired a pro to come to my house and replace the windshield on my 68 hardtop. Same deal though, the gap will be larger than original unless the installer knows the tricks and does it right.
When all was said and done, there was still a slight noticeable gap (to me) between the new glass and the original chrome trim.
'68 428 HO M3 Monster, 4-on-the-floor! Need I say more?