What engine for my new Town Panel?

So i bought this 1964 Dodge Power Wagon Town Panel. It has 55k original miles, as far as I can tell it has the original slant six engine and 3 speed column shift transmission. It was restored and painted once, around 1997 or so. It has been out in Nevada for a while so the paint is peeling, and it has a couple of spots where old body work is cracking. All in all the truck is in great shape.

I sold my 2014 Challenger RT and my little Ford Ranger, so this is my daily driver. My goal for the truck is to set it up as a people hauler. It currently has a nicely done minivan seat as the middle row. From the factory these could have 3 rows of seats so that is the plan. I'm thinking maybe 3 rows of captains chairs, or going back to a bench with flip up passenger seat in the front. I'm going to put in carpet in the back to cover the wood floor, and add A/C and a radio. Eventually it will need power brakes and power steering, I will possibly swap to disk brakes, but I have not researched doing that with 8 lug wheels.

My dilemma is that while I like the truck a lot, this 3 speed is terrible, and with the 4.10 rear it really feels like it is struggling to move under it's own weight at times. I can see why the truck has so few miles. Basically this thing needs to be altered to be really driveable. I want to be able to take this thing on vacations. I want to be able tow a utility trailer, small boat, or maybe a fairly light car hauler. I want to keep the 4wd, but it is a divorced transfer case, so that doesn't really seem to matter much. I want to be able to drive this thing to the beach, or the mountains, distant car shows, etc.

So I'm saving about 550 bucks a month not paying a car payment and insurance on the Challenger, so if I save a couple of months I have some money to work with. I have thought about a couple of engine combos. I' sure a diesel would be just about perfect in this thing, but I'm ruling that out, as it seems to be more fabrication work than I want to do.

So from my research it looks like I can pick up an overdrive a833od and hook that up to any of the three engines I was thinking about. If I'm missing a better transmission option someone please fill me in, the 833 looks like it should be a drop in on this truck. I see the Passon 855 also, but I don't think I want to spend that kind of money yet, and that might still be an upgrade option later if the 833 is lacking.

Engine options....
5.7 Hemi swap, most expensive, but would give me plenty of power in stock form.
Original slant 6, switch to EFI, hang a turbo off the side. Probably run megasquirt.
5.2 magnum swap. Sort of splitting the difference here. I'm guessing this would be cheapest. I'm thinking this would probably be worse mpg and worse horsepower than the hemi option, but cheaper if I can find one in good shape.

I want power, reliability, parts availability, etc.