To answer the question about taking the gearbox out, yes, as soon as you remove the prop shaft, the gearbox oil will drain out, especially when you tilt the gearbox. How do I know? Well I turned my lino floored garage into a skating rink when I first did this many years ago . Definitely take loads of photos - more than you think as it's so easy to forget how something fitted. Location of wiring harness, brake pipes, fuel line to engine (and return). Label everything carefully in a way that can't be easily damaged - I used masking tape which I wrote on with biro but if I got fluids on it, it became unreadable so use something better. While the chassis is at Arch, do have the panels powder coated on the inside - makes a massive difference.