Funny, the HJ ID plates on my website off a 1900 coloured Sandman also came off a van destined for the scrapyard. Well it was in a scrapyard. Difference is I left it there as it was too rusty (in those days!). Today it'll pull $5,000 on Ebay. Only difference is it was a 308 M21 and 3/76 whereas yours would be an 11/75.
Can you post the chassis number for the Sandman database? Should be around BHJ20750B. I have a fair few holes in the database, and this one sits in the middle of one in chassis numbers - it would fill up a hole nicely!