I too use the Lomo tanks, but I have never tried using the top like that Nick. It so happens that I have about 12 carts of super8 to do, so I'll give it a go. I have 4 - 50' tanks and a smaller Meopta one for 16mm (D8) which only holds about 30'. All of them have clear reels. David, just remember that the emulsion side faces out instead of in - I don't know why. Also, I find 16mm the easiest to load, and two layers of super8 that hardest. I would appreciate any other hints anyone may have. The tanks don't leak light, but the lid can come off is one is not vigilant. There is a small hole/drain/ in the light trap at the top of the spindle, which may possibly leak light, but it can be masked with a bit of gaffer's tape.
Cheers,
Clarence