This is a topic that has seen quite a bit of discussion lately. The general consensus from those who have done it is that it is not worth the extra effort over something like a 4.0 or 5.0 to swap in a 300-6. They are long, they are slow, and they get terrible gas mileage.
I haven't actually seen one completed and driveable yet.... though lots of people have talked about it.
The 300-6 is a great motor for what it is, but it's long, heavy, and will not generate the same results as a 5.0 swap. The one thing that makes a 5.0 swap easy is that since Ford put it in the Explorer, they had to shorten things up to give some extra room for things. That can help a lot in an engine swap. I have seen Rangers and BIIs done with the full-length components, but after having done a 5.0 swap into a Ranger myself (a project between myself and my dad), having those shorter components on the front made things a lot easier. No messing with whacky motor mount settings, no bashing the firewall, it just fit.
No such components were made for the 300-6. And it's a longer block than a 5.0 because it's an inline motor. The 5.0 only sports 4 cylinders deep since it has 4 on each side of the block. The 300-6 is 6 cylinders long.
My cousin has a blazer with a 4.3...Had a bent valve when he bought it, got that fixed. Then on the way to Pennsylvania it threw a rod on him. Had to replace the whole engine. I'd take a 4.0 over a 4.3 for sure.