But also, and this is more of a challenge, windows that open so you can smell and (just about) hear the "engine" going "chuff chuff toot toot".
Thus, if you stuck Mk4s behind it (or something), even if you paint them maroon and stick fake doorhandles on the outside, the appeal would be reduced.
It is possible to retrofit opening windows to late Mk2 stock, to be fair, Virgin did it (for the inevitable aircon failures) on the WCML sets. But anything later than that would seem to miss the point a bit. Having said that, didn't Ireland have fresh air Mk3s so retrofitting those with openers might be an option?