My concern over the fork would be if you can get it firm enough for Tandem use. A lot more %age of weight is put on a Tandem front end than on a solo. I Use rockshox Boxers with the hardest springs- Maximum sag adjusters to give it less movement and use a heavier grade oil in it. Still use the whole 6" of travel on the downhills though. Second on the fork would be The wheel fixing. If using Disc brakes- it is preferable to have a Bolt through axle and not quick release.
On the wheels- If you are going offroad- then the wheels will take some punishment. Rims should be up to "Freeride" standard. Hubs will still take some punishment aswell so don't go too low a quality on the wheels.
Attachment is of the front end of our "Offroad" Dale MT2000- and this one does work offroad.
Boxer Forks- Hope Mono M4 disc's and Hope Bigun hubs on Mavic Downhill rims with 36 spokes.
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How long was I in the army? Five foot seven.
Spike Milligan