Well Andy, can I congratulate you on doing the biz with your car. (That's me being serious for once, by the way.) You're right in that your hypothetical £35K would be better being put toward an LB or Hawk, but if you've not got £50K+ and you really want a Stratos, your options are very limited... The advantage to Ste's car is that it's actually running and driving, so it's not simply a pile of bits. Personally I'd not bother with the Busso motor and tweak the twink it's already got, but that's a decision for the buyer (or Ste if he ends up keeping it).
Advantage of your car is it's already registered, but against that it's still a rebuild in progress.

But are Strat reps really "vastly inflated" or are you referring to old classics in general? If you want a turnkey Hawk or LB with a Busso V6 you'll be looking at over £80K. As a kit, I dunno, about £40K or more for the full skipload of parts, but then you have to build it, paint it, trim it, source a donor, blah blah blah. Face it, a good kit ain't cheap, and if yours was £23K back in the day, that too was a good chunk of loot. My Integrale was £25K new back in 1992...the Allora I did cost me £12 or 13K by the time it was finished in '89. As a running, registered car you could ask £35K for it now if it was still in decent nick. And Littons, CAEs and Napiersports will be about the same, IF they're in good condition and properly finished and presented.

So - ARE you selling yours too, or just toying with the idea from your jail cell after using an A40 starting handle to beat the cr*p out of the thickos who can't string a sentence together?