A couple of thoughts from someone who has been down this path before. I was involved in some of the early design for the ACE D2 LS kit. The Disco is not an easy car to swap, particularly from scratch. To do it correctly in my opinion, you really have to think about everything as a system starting with the axles and work forward from there.
The axles are offset to the passenger side front/rear, which is a somewhat uncommon configuration for modern-day stuff. This means you have limited transfer case options. Center output rear transfer boxes would be require a somewhat extreme rear driveshaft sideways angle that would likely cause excess vibration, which makes most other options not usable for a daily driver.
The LT230 is a pretty stout transfer case, all things considered, and already bolts into the frame, making it somewhat of a logical choice. It can move back a couple inches before driveshaft lengths start to become a problem. It also can be converted to selectable 2/4wd (not that I would really recommend that in the short wheelbase Disco though). Overall package length is important - With the ACE swap, it was great to be able to get the engine to sit far enough back that a viscous fan could still be used in the front and for weight distribution / driving dynamics.
The Volvo engine you mentioned I believe(?) were all used in transverse applications. It would be easier to start with an engine designed for longitudinal applications. I personally feel like going that route is asking for more work (just look at the trussmount setup Cody Built manufactures to fit transverse VW TDIs into Jeeps). Also, you need to consider potential oil pan clearance issues with the front diff and front driveshaft. A transverse engine may require a heavily modified or custom pan.
As for the electrical side, make sure the engine you choose has a lot of aftermarket support, particularly tuners that support building standalone engine harnesses and standalone ECU operation, so you don’t need all the body modules from the donor car. Having to drag along clusters from donor vehicles is a major pain and wiring nightmare.
Point is, before you buy anything, try to have as much as you can planned out. This is nothing short of a massive undertaking to do correctly. 100s of hours for research, then execution.
If / when you get to the Discovery electrical part, I helped ACE with their Gen 5 /6L80 Disco electronics interface as well as some other engine swaps in D2s. Happy to help as able.