Value of big iron

The Curator of the Computing Collection at the (UK) Science Museum is coming down to see it in May to see my second ICT1301 to give me a provisional decision on whether they want to take it. If they don't, I have found someone as mad as me, who would like to buy it, but he want me to give him a price. My question is, how much is it worth? I don't want to ask too much but I don't want to find something similar is sold a couple of months later for ten times as much. I have two bracketing values, that I bought it for 150 GBP in 1977, and that it was sold new for 247,000 GBP in 1962, both figures plus inflation of course. That is a somewhat wide range, and must be reduced by the fact it is not assembled and will probably need many months work to get it into working condition, but even as a static display it is quite impressive. Does anyone know of any experts who could come down and value such an unusual thing? Probably none have been sold since I bought mine so it would have to be based on other brands or models. Roger Holmes