So its really hard to tell a 68 R code car just at a glance...it was an engine option, so it could be a fancy "GT" version with the C stripe and the hood stripe....like this:
View attachment 195757
or a totally plain version like this (factory lightweight car)
View attachment 195758
They only built ~1000 68 1/2 (it was only a half year option) R code cars so they are very rare and VERY valuable, much more than my 67......So I would be surprised if someone took a real one and put flares, fake hood scoop, etc....but if you really want to know at a car show....just look here....vin is stamped in that spot...5th digit (letter) on the vin..
R=428
S=390
J=302
View attachment 195761
probably a 390 car that someone upgraded....a 390 and a 428 are like a 396 and a 427...physically the same engine, so they can easily be swapped.
as far as whether or not its a real 428CJ engine...thats really hard to tell from the outside...few stamped numbers here and there, but the blocks look identical to a 390. Plus they also made like 6 different versions of just the 428, and 100 other FE variations....427s with cross bolted mains are really the only ones that are easy to ID when looking under the hood at a carshow.