That first link looks good. The only reason I went with the Toyota box was price. Yeah the steering shaft should line up & fit straight onto a defender steering column, easy to make & weld those brackets to hold the box & you don't need to mod the front Xmember like I did. If I was to do it again I'd do it the same way as long as I could get the parts cheap enough plus you won't have to X-ray anything as it should be pretty much a bolt on except the brackets welded for the box. The steering shaft will be collapsible being modern usually. Just means it's 2 piece slides inside one so much easier. Yeah I'd go for that. The only concern I can see is the pitman arm. Arm at the bottom of the box , being straight you will just have to make sure when the balljoint is on that it doesn't hit the bottom of the chassis but you can either tilt the box or notch the chassis. Yeah that be easier & quicker conversion to do. & the drag link will need to be shortened to suit the series track. To easy if you have all the parts I'd say a weekend in the shed would get it done. Yes I quiet like that setup.
The second link I have most of everything on that site printed out.

