Thanks for the advice - in hindsight we were probably being too exact.

Here's the belt fitted, matching some other images I just found in some recent threads (the distributor thread immediately below this one helped). The pulleys don't exactly line up, but they're almost the same offset from the horizontal line:







We used the old gasket and head bolts to test the cam timing - we put a dab of copper grease on the top of each piston, where the valves would touch if it were out, put it back together with the belt setup as above and turned it over 2 full revolutions ... no unusual resistance.... then took the head back off - no grease transferred to the valves. So we are fairly confident that the cam timing is now right.

Thanks again for the tips. I'm used to modern engines that have dowel or pin that fits the cam to the correct location, so not having anything to set it to a fixed point was a little concerning when the timing marks didn't line up!