thanks guys, for your thoughts.
DC - the pencil lines I've marked (shown in pics) try to follow the upper growth ring on each side at one end for the full length of the board. On both sides, that ring remains within the board for the full length, and leaves 17 mm (11/16 in) on one side and more on the other. The basic ELB plan I had required 12 mm (15/32 in) depth, so I was thinking this would be OK.
The problem is, it looks as though the grain line dips more on one side than the other, meaning the back will have a twist if I follow it perfectly.
Gifford - thanks for checking out the species. Glad it's a good one. I did trace the lines (in the pic) and they remain in the board. But I agree, have a go, then go again if it fails!!
Stuckinthemud / Bassman - OK, so growth rings running from back to belly. I'll give that some thought too.
Aaron - the board does have growth rings running the full length, and within the board, on both sides. I figured on that basis (with my limited experience) that it would be OK. In hindsight, maybe more thorough inspection and tracing individual lines all the way whilst in store might have helped. Was the only one they had too. And I'm super keen to get on with making shavings whilst I wait for 'real' staves which I'm collecting to season.
TimBo - good call indeed. One end still has the sealant on it. I'll clean both ends properly and re-assess.
Woodley - not sure I have the width for a quarter saw. It's only 50 mm wide. I need 30 mm at least in the handle.