Hi Stefan. I'm afraid there was very little in the way of custom ordering available from Dawes at this point in their history - although having said that they did include a couple of bare framesets in their catalogue (might even have been 1982). I used to work in a bike shop that ran the Dawes range at around this time and was lucky enough to get my 1st Imperial as a warranty replacement (with a bit of leaning on the sales rep by my boss I think) after I cracked a rear dropout on a lesser Dawes I'd bough 2nd hand. They also later did me a custom colour on a Ranger frameset but this was not a regular occurrence. Somewhere I posted the summary I did of the specifications of all Imperials from 1982 to 1986 but I can't remember where, so have uploaded a pdf of it for you. This pearl red was the same as the ladies "Fleur" model of that year. I see that I don't have any evidence of what headset was fitted to the 1982 model - though later ones were alloy.
Restomod, eh? Nothing wrong with that. I have 2 imperials, one as original as I can make it and the other "as I would have improved it" in the 1980s. I can't argue that modern indexed gears and brakes aren't better so go for it! It's sometimes a bit of a challenge to find modern bits that still "look right" to my eye but there's no reason to be stuck in the past. The key is understated subtlety; Even in their sunburst paint job years, Dawes were never flash.
I don't think it needs it but if you are contemplating a paint job, Lloyds do all the decals.
The original SR handlebar stems come up often on ebay and polish up very nicely if you can be bothered.
The CT-5LA chainset had an unhelpful 144 BCD, which I think limits you to a 41T inner ring so a good candidate for upgrade.
If you decide to migrate the Shimano stuff to the Galaxy (cheeky suggestion), the Cyclone II gear mechs are worth seeking out and were superbe (Not "Superbe" which was a more upmarket Suntour groupset and would look fantastic on this if you can find one. A few NOS sets pop up from time to time). NOS Cyclone II seem to pop up quite a bit your side of the pond.
If you stick with the Weinmann brakes, they were excellent in their day and very easy to service, but will never have the power of a disc brake setup.
Original saddles are hen's teeth and not worth the money (imagine plastic razor blade) and the same is true of the Benotto-style handlebar tape.
You're not missing anything special by not having the wheels. The Atom hubs are fine but nothing much above ordinary although the Weinmann 571s rims were better than on later models. Spokes were never stainless but 1986 models had chrome double butted ones (which rust if not maintained). For a restomod, you might want to look at sticking on some Rigida DP18s?
I think you'll find the Imperial a pleasant surprise as compared with your Galaxy. It's 531 throughout and has a marginally more upright geometry (you should find a "73" stamp at the top of the seat tube indicating 73 degrees parallel - the Galaxy was 72 iirc) and a shorter wheelbase making for a responsive ride.
Anyway, good luck with your rebuild and shout if I can help in any way.
... very nice sparkle to the metallic "pearl red" (it's more of a dark rose/pink to be honest, but I dig it!) 
