Hey RSR -
What I did was get a heap of stuff precut when I ordered the steel in order to avoid a heap of cuttin with a hand grinder, resulting in crooked cuts and the like.
The 50x50 square box section for the swingarms and uprights were 450mmx2 (spare upright and 45degree brace) 150mmx2 (to hold the traingular plate for the wheel bolts off the upright) 550mmx2 for the swingarms (although I would get maybe 600 to make using the hole saw easier [this leaves room to still put a trailer on the towbar]) 200mmx2 (for the bottom of the main beam end sections)
2x 50mm lengths of 20mm solid rod for the securing pins.
Some of the other material used was a triangular piece of 5mm plate (the 2 short sides being 150mm) this was used to weld the high tensile bolts into drilled holes which then all support the spare wheel.
Re: the spare wheel holder assembly, call me and I will explain the exact alignments and what not, it's actually fairly straight forward, but easier said than written)
2 lengths of 2mm thick 50x20mm RHS for the uprights of the jerry holder. I used 280mm for mine, (but that may be different if you go down the folded sheet steel road ) 1x135mm (cut diagonally to make the bracing gussets for the base of the jerry holder)
One sheet of 2mm plate the size of the base of the holder (360x185mm).
I also used some 50x5mm plate in a couple of lengths(have to remeasure) for the vertical ends of the swingarms as wells as for the bent horizontal sections that hold the latches and the holes for the securing pins.
Those 8mm straps going to the tow bar mounts needed to be bent to align properly and a small section about 10mm was used to fill out the gap between the strap and the main beam. ( call me on this one as it's a little difficult to explain)
Some 50x2mm plate is handy as well in order to cap off the spare upright and to raise the latch hooks off the reo to a level where the latch (being mounted on the 5mm plate) will come in horizontally level, as these need to be aligned to actually funstion properly).
You might also need a bitt of plate to drop from the hook plate down to the 60mm RHS that the 20mm pins are welded to.
Looking back on it, the jerry can holder I should have made out of folded sheet steel with a slot cut out on one side so that a water jerry with a tap can be lowered in at an angle. therefore exposing the tap at the base and giving easy access to water without having to remove tha can.
Confucius say: always remember the 6 P's - Planning & Preparation Prevent Piss Poor Performance....
I see what you mean about having a few drinks in between 
It was a little warm today and I had to keep the fluids up 
Maybe it's something to do with the work connection here, it's a bit screwy sometimes in terms of allowed content. :/