For the life of me I can't remember where Agrover's posts might be, it was a pretty neat setup. I've thought about making my own as well, having made a number of industrial reduction boxes on the fly.
Eight lug... It's so simple, no worries about wheel selection, being a vendor of Rover stuff I would be tempted to try and retain the 5X6.5" bolt pattern, anything can be made.
It's on LR4x4 I believe but the pic's got lost a while ago. However, I happen to have a full set saved along with the text
As you say, anything can be made.... just cost to get castings or CNC machining for the housing is the killer for poor mans portals. I wonder if you can sweat & TIG weld a spur gear onto a 110HD CV outer, would just have to support the 'socket' end then for use as the lower output shaft assy or find a bearing that would fit the CV OD.
Using laminated, dowelled & TIG plates seems to be a good 'cheap' option, have found a local'ish company that waterjet cuts plate. On 0.5" thickness the accuracy is more than adequate for either leaving holes plain for bolts or just requiring final reaming for dowels. Bearing aperatures would need a clean up in the lathe but that's no biggie in a 4 jaw chuck for a machinist. Best part is you don't get the localised hardening as you do with laser cutting, makes post machining easier & cheaper.
This might be just the thing to go learn Solidworks with.
Ummmm..... ideas ?