Really depends on how much you are willing to spend and how deep you want to go. I've done 2 radically different hemi swaps now, and own 4 hemi powered vehicles so I know a little of the pitfalls and benefits.

For transmissions you could stay with your 904 or 727, and simply buy a SFI flexplate that will allow the hemi to be bolted up to your existing drivetrain. I would assume you have a decent setup already so that would help in reducing some cost. Pending what modern trans you are looking at, the NAG1 seems to hold up to some pretty serious cubes and power adders, but while the 545rfe is a stout trans, I know in the truck world guys that are hitting them with big cube hemi's they don't last too long. Now they are pushing 4500+ lbs trucks, so your rig they might last longer.

For the motor, again depends if you want to keep the fuel injection, or run carb? On my one hemi swap (in a '87 W100) I went with it bolted to the 727, and I converted it over to carb. There are carb swap manifolds available (edelbrock dual quad, Ritter high rise, mopar has a hemi specific intake, etc) but they are all in the neighbourhood of $1k. That was too rich for my blood so I built a sheetmetal carb manifold myself. For engine control, I'm running an MSD Hemi-6 that will control the spark for you. Really nice setup, and you can build your own timing curve via the computer then import it to the MSD box. This setup (carb and MSD) is very simple to use, and it is more conventional hot rodder tuning friendly.

The other option if you want to go fuel injection and modern trans, is to use a complete harness from a donor vehicle, or go somewhere like HotwireAuto, and they can make you a harness for pretty much any combination that you want to run. Again they are a sweet setup, but for me way too much money. With this setup you will also have to be reliant on OBD tuning so will require a tuner like Diablo and have someone tune for you. You could also buy a Megasquirt 3 system and build your own harness and then you can do you own engine tuning, but will have to stay with old trans, as there is no transmission control functions in the Megasquirt that I'm aware of. I seriously considered buying this system, but haven't as of yet. Additionally if you want to go with fuel injection, you will need to upgrade your entire fuel system.

My second swap I am doing is I'm putting a 5.7 hemi and 545rfe trans in a '74 W100. This build I'm keeping all the factory wiring, and it's working out great. I have the swap all done, and the truck running, just need to get the drivetrain and other misc items finished up.

As for making big power I'm not your guy for that. In my '07 Power Wagon, I'm running a KRC 210X grind (I don't know the specs off the top of my head, but I have the cam card somewhere) and on 108LSA is sure sound pretty nice and it does pull hard. Tuning has been a little challenging getting a tuner to do what I need, and with my truck being a 6 spd manual there is not a lot of tuners tuning experience with that trans. Definitely has a good broad torque curve and that's pushing a truck that weights 7500lbs. The hemi's do respond quite nicely with cam and head work as long as you have the supporting tuning!

End of the day there is a TON of information out there on hemi swaps, and all different routes pending how deep your pocket books are what direction you want to go. To hit 10s and have it as a track only vehicle, I would go a with the stock displacement, upgrade to a good forged crank and pistons and hit it with a big shot of nitrous or boost and let it rev. Oh and I would stay 904 or 727 manly just for cost.