Hi Joe,
Good to see you have made a start. Nice find with the post office bikes, I thought of using a shopping trolly basket for mine at first! this could still be an option? Just cut the wobbly wheels of and weld up the flappy bit.

Make sure that the forks you have actually fit around your back wheel? - remember your back wheel is wider than a pair of front forks due to the cogs etc

Youv'e probably already seen my cobbled together hitch - (wider than the back wheel)



As yet still untested. I'll try and get a couple of pics done to show you it hooked up.

Keep updating your progress mate, I'd like to see how your getting on

Regards
Tom