The Levinson 28 was, IIRC, the only preamp that hifi dave would regard as a possible step up from the Crofts of the period, although Amar's all but taking over the business and making Glenn innaccessible may have had a part too. I liked the 28 though and £800 is a good price for a clean one IMO. It may need to be left on for the fully balanced circuitry to stabilise though.
What about EAR? The deluxe version of their baby preamp comes up for around this sort of money and apparently it responds well to tube-rolling.
I won't waste my time in recommending the later AVI preamp, which is well put together and has a very accurate and faithful-to-source line stage in it, as it may sound too clean-n-clear for the bods on here.....
Tear down these walls; Cut the ties that held me
Crying out at the top of my voice; Tell me now if you can hear me