That appears to be a 1973-1975 P10 Paramount. If the stand-over height is correct, a 24" frame sounds about right. It appears that the owner has placed tape under the mounting points of the rear rack, so hopefully they won't be any damage there.
That is an early Brooks Pro and in that condition they go for $100 +/- on eBay. If that frame fit me and the condition was good, I'd give $500 for it all day long.