Hexagon are always pretty bullish on prices but seem to achieve it for the best cars. Assuming this has been recommissioned and has a new soft top (I can't see the original being of much use after all those years) I'm sure they'll get that price or close to it - look at the prices for the best 107s on the SL Shop's site (a restored 300 for £100k and a 5,000 mile 420 for £79k) and other leading specialists
Personally I'd rather have a low mileage, mint SL60 and an accompanying SL600, but I just prefer the R129s