I have an 85- F-350 Dually 4x4 with the 4.9L straight six. I am wondering what years I can use to switch out the long-block after a co-worker overheated it. Is there any reason why I can't use a newer Fuel Injected engine as a long block ??? Any help on the years I could use would be helpful.

ok..first off...the 300's are PIGS..they will take all kinds of abuse..make sure its dead..its all Iron..so heat doesnt really warp it too much..

as for the swap...

the newer EFI engines use a slightly larger thermostat housing (got the gasket for a new one and it wouldnt seal right) but everything else is the same..just unbolt..and install..

I've heard that the later castings (especially the EFI ones) are more susceptible to head cracking/warpage. My 80 casting took 280* temps twice with no noticeable affects. Still running strong.
AFAIK, the 240/300 all interchange with the noted exception from wanderer. Get a 240 head and slap on your 300 for about a 1 point increase in compression.
If you rebuild one completely, you can use 351w pistons, if you bush the 300 rods, for a variety of compressions.
There is a large community of 300 devotees with a wealth of info on tuning the big6. Do a search on the Ford-truck forum for a LOT of info.

block shows to be the same from 65-88. Anything from a van to a truck is the same. 65-74 was only a 240 but it was the same block. It changed to fuel injection in 87 but the block stayed the same until 89.

Well, I had a 65 with a 300 in it. Factory original.
The 240 and 300 were produced side by side until the 240 was discontinued for automotive use (possibly 74?), but I have seen late 70's equipment with 240 engines.
IIRC, the 240 was the base engine in 2wd 1/2 ton trucks in the 60s. The 300 was an option, but I've never personally seen an original 300 4wd truck before 73.
Quite possible, though.