The main thing that is preffered about the earlier vikings is their wire ball detents. Wire ball detents have proven reliable and easy to adjust over the years..the 04's have those spring loaded plastic nubs under the eye covers and they are just more of a hassle. Really thats it.
Ive always considered the stock LPR on vikings to be just fine..scm isnt really neccesary. If the 04 has the built in LPR honestly it should be more than good enough.
Ive had 2 04's and no earlier models. Id probably get the cheapest one now..but id rather have humphrey solenoids.
All 04's have humphreys, some 03's do. Either solenoid works fine. Just try and sell both and keep the one that doesnt sell if what id do.