Thanks for your reply Barry. As Grant says - Great answer.
I haven't come across the GB mounting block and that certainly looks more rigid than the block which the Decca is currently fitted into and may be something for me to consider.

I'll take the headshell off and weigh that, so I can see what I'm dealing with.

Although I am using the "wedge" shaped Ortofon headshell (as shown in the manual you kindly scanned) I had to remove the straight, semi-circular fingerlift as the fixing of that compromised the Decca mounting block. I utilise a propreitary fingerlift that bolts through & fixes above. Although it works - it does look a dog's breakfast.

I will also search out a photo of the present arrangement - for you to have a laugh at !

Regards,

Mark.