Thanks for the advice and links guys. Armed with that knowledge I was able to fit the engine today.
I couldn't find a completely satisfactory way of mounting the gearbox so the end result is a bit shocking...
The seats are ready to go in, I'm just waiting for some threaded inserts I need to weld in to the cross/support bars. Hopefully tomorrow.
The tank support/rear panel frame is tacked together and I've made a start on the steering column. I'm pushing to get the chassis complete as soon as possible before our little one arrives but I keep remembering more bits to weld onto it!