I think FRF Volvo Parts Department are the helpful Volvo dealer often mentioned in the forum as giving good service and good prices.
They tell me that the correct part number for the 240 battery is 30659797 now. They spoke with an office within Volvo to check that. The new part number battery is also used in
eg some 440 and some 740. It is 520 CCA, the original was 440.
And they say from looking on Google Images that the terminal positions are what is needed for my 240SE, with the terminals closest to oneself, negative is on the left. Here's a link to a picture and the part number can be seen in the image.
Volvo battery part number 30659797 from Google Images
They charge £62.88 after discount. Unfortunately they're a long way away from me and they can't send batteries out by carrier.
I can get it delivered from a more local dealer's by their van for £68.78 after discount. They are just going by the part number I have given to them and they say if it's wrong they can't send it back. So if anyone can confirm or deny the part number as being suitable I will be grateful please.
I'm basically convinced anyway. It's a Volvo car battery so the width will I'm told be right to fit the baseplate, and the Google image shows the terminals as corect. Here's hoping ...