On a working F40 the voltage is about 103v. For starting the 80w merc lamp needs less than 240v (since they start on line voltage with 240v), i did not find he OCV written anywhere but i dont expect problem with too low OCV failing to strike the lamp
Look at this one - it is perfect (2 of those)
http://www.radionic.net/D340TP_P2614.cfmThough a bit more expensive
If you buy the D340TP Preheat ballast wiring is straightforward, just measure to make sure they are really in phase and nothing unexpected is going on
As for the ballast that you found, it have a downside in that it have 4 wires coming to te lamp. This makes the use of the ballast more complicated and requires more testing to be done because of one more possible issue present - shorting out the heating coils of the ballasts against each other. This is the same order of complexity like using 2 2-lamp ballasts, so if you have a few 2-lamp ballasts on hand you won't save much efforts by buying this, an can save the expense....
But i think it would be possile to test with those ballasts as well, worst that can happen is that the testing will show that the ballasts are not usable for running the merc lamp but youll be able to use them for other purposes...
If you buy the ballast you found in the 1st place, post a note before you go powering up the mercuy lamp so we can take the multimeter to find out more about the ballast's internals. And if you are buying this check out the price, they are listed for 13$ in Radionic's website might be cheaper to get from there depending on postage...