Hi.
Also very sorry to hear someone else has a had a bad day on the road.
I cant find any M21's for sale at the mo but the following M20's are on ebay
1954 Civilian model £3799. I would suggest that is not far off But?
??
1942 Military WM20 £6250. I think that is a very unlikely price but you never know.
If I was your friend I would be looking at least about those sort (£4500)as a start point but I think that they are unlikely to pay that much out. Unless he can possibly prove a higher value.
This is` where agreed valuation comes in very handy
Mike