One upgrade I knew I was doing from the start was switching from a dynamo/generator to a modern alternator. I read all the pros & cons and found this to be the best way to go. We had to make a custom bracket to hold it properly, and after painting that, it looked stock.
All of my wiring came from British Wiring, they have all the harnesses (in both PVC & cloth) along with all the other necessary items - bullets ends, connectors, properly colored wire, grommets, etc...
After initially getting the cloth harness, and having finished most of the systems on the Rover, the genuine high beam switch on the floor decided to short and fried most of the harness in the dash. It was a time crunch after that happened (was showing it that weekend), so I had to go with PVC for the replacement. When replacing it, we also added a lot more fuses. The original fuse box holds just two fuses; one for the dash lighting and one for the interior roof light. Not much protection. To make sure I didn't have to see think smoke pouring out of the dash again, I fused pretty much everything. The ignition wires each got one inside the dash. And in the engine compartment, we came up with a way to keep our new original Lucas fuse box and still add a fuse for each of those green wires. It looked cool and works great.
I also upgraded the headlights to use relays. They were simple to setup, and would have been done quickly, but a bad ground delayed us for probably an hour.
After fixing that initial bad ground issue, I decided to overkill the grounding too. Using some modern grounding straps from a Ford, I grounded each side of the rear lights to the chassis, the front grille, and one for the bulkhead too - that was in addition to the standard starter ground.
Going back to the alternator upgrade, it was very simple. The harness I ordered had the alternator mod already done. My modern CS130 alternator didn't work with the standard plug, so I ordered a CS130 harness and just soldered it into the engine harness. It worked great, I have my charge light working properly and it runs at 13.5 - 14V consistently.
For most of the soldering, we used a small butane torch, it was awesome. I didn't want to just crimp everything, so we soldered everywhere we needed to. A lot of the lights had wires that were just too long, so on those we'd cut to size and then put on new bullets. The torch would get the solder flowing in a second, and it made soldering the bullets a snap. We would wrap the exposed wire in about an inch or two of solder and then dip it in flux, then put the bullet on and heat the entire thing until you could see that the solder had liquefied. That created a really strong connection. I actually had wire break when trying to remove the bullets from a connector.
The bullet connectors have to be one of the worst parts of the whole electrical install, they are a pain to connect especially in some of the areas you need to. I wasn't able to get the bullet connecting tool, so they were all done by hand with a screwdriver and pliers to help.
And one other note, I found the electrical diagrams in the Rovers North catalog to be better than the ones in my Green Bible.