Putting the V-8 in is the easiest part of this operation. It's all of the other modifications you have to make that takes a lot of time. To have a V-8 in an AD you need to modify the steering if not change it all together. You need to come up with an engine crossmember to support and mount the engine to, which a lot of companies now produce. I had to "clearance" the firewall to make room for the distributor and modify the brake pedal and rod to clear the left side exhaust not to mention I had to convert mine to 12 volts too. You need a GOOD radiator not one that's half plugged from 40+ years of junk.
Now, to bolt the V-8 into your truck, I would suggest removing the whole front clip, there will be alot of modifications to do and this makes it a whole lot easier. I used a mid-70's bellhousing with the starter area notched to fit the block mounted starter. The mounts will need to be adapted but I mounted it into the original bell's location so I wouldn't have to rework the drive shaft. I installed a mid-70's V-8 also, so I used it's original exhaust manifolds only needing to slightly notch the right one to fit. I made my own cross member, but I would suggest buying one, saves time and money in the long run. The clutch was from an 80's 1 ton that had the same spline count as the original 48 had.
There's a lot of work to be done over and beyond installing the V-8, and if you are still up for it, keep asking questions. It's been a long time since I finished mine so I may need a nudge to remember some of the details. I still use the truck often, so I can go to it for reference still.
Good luck which ever way you go,
Scott
And thanks for the plug OldSub!
