I reckon that's pretty decent Lindsay.
With the same later iron head as yours, with the same book-settings 389, and flat top pistons, I usually managed somewhere in the mid 60's mpg, but could squeeze close to 70mpg if running gently. I weigh quite a lot and present a more challenging profile than you do (as you know!) so I was always pretty pleased with the A's economy. When exercised a bit, she'd still do 55+mpg.
My local mate her current owner regularly runs her in the 70mph range with bursts to 80+ omigawd (I never did much of that, 60-65 were enough!), and reports the metric equivalent of 55mpg too.
His fuel costs will no doubt pale by comparison with his engine overhaul costs in due course, but she's been run quite hard for several years now and nothing bad has happened. Yet. Those IMG pistons I stuffed in prior to passing her on seem to be doing a good job!
Luckily, my said mate is very well-equipped to fix it when it goes bang one day as classic repairs and restoration are his game.