Yep - that's the adapter you need.
For mating the AX15 to a D300, you'd just need a clocking ring - usually about $100. Many places carry them, some are better quality than others.
You're getting into a whole new bag of worms with an engine swap no matter what, but at least with the 4.0/AX15 you might be able to get them both together for not too much money. For the Chevy swap, from experience, it's going to run you probably double - but the thrill is easily double as well, and probably quadruples what you have in there now.
There are a lot of members here who've done all sorts of drivetrain swaps. Some of the more common are the 4.0/AX15 and the 5.3LS/4L60e(auto) for example, with every variation in between. I swapped a 5.3/AX15 and it probably ran me close to $5-6000 all said and done. I"m not sure if I'd do it again, but it's a lot of fun compared to the 6cyl I had previously.
Best to sit down and give it some thought like I said. I don't even want to remotely convince you of a complete drivetrain swap, you have to first decide what you want and how much you want to spend. With an engine/tranny swap you'll have to plan for driveshaft changes, installation, adapters, engine mounts, wiring harness, and maybe even gearing changes. The T176 swap starts to look comparably simple and cheap.