Component replacement is definitely DIYable and not that difficult. If you are replacing the full system, you can do most if it in your yard with simple tools.
You need to add an Oriface Tube to your list of parts (that might be the filters you mentioned). IMO I'd probably add Evaporator as well since it's under the hood and fairly easy to access with the 4 cylinder I think.
First step is evacuating the system. Unless you know for certain that it has all leaked out and there is no residual charge on the system you'll need to take the truck to a place that services ACs and have them evacuate the system. It's illegal to dump refridgerant to the atmosphere.
Once that is done about the only special tool you'll need are the line disconnect tools. If you were going to swap the clutch over to the new compressor you'd need a few more, but I'd really recommend replacing both as an assembly.
You will need to add PAG oil to the reciever and compressor when reassembling the system. You'll have to search around for quantity, but it should be covered in a tech library article.
Purging referrs to one of two things. Either evacuating the existing coolant out of the system before servicing it, or pulling a vacuum on the system after servicing. Basically for the latter you'll pull the system down to 30" of mercury and let it sit at that vacuum for a period of time with the pump attached. This will boil off any residual moisture in the air that entered the system or accumulated there over the years. After letting the pump run for long enough to do that, let it sit under vacuum (without the pump) to see if there are any leaks. Basically if it still reads 30" the next morning you've got a tight, leak free system.
There are instruction around for how to charge the system. I'd recommend taking it to the shop for recharging. That requires special tooling like a set of manifold gauges and vacuum pump. In my experience the rentals available at the auto parts stores are not good enough to do the job. I have the tooling now, but I'm stupid like that. Would have been cheaper to take it to the shop and let them charge it. My justification is that I'll have a few more to do in the coming years with my other trucks (A/C retrofit in the '68 and unknown condition on the '85).
I don't know if it is necessary, but after reinstalling the components I'd leave the compressor clutch unplugged or pull the clutch relay until you are ready to charge it. Doing so will prevent the clutch from being able to engage and potentially burning up the new compressor.
Honestly with all new components and them doing the work $800 doesn't sound bad. To DIY component replacement alone, you're looking at $300+ worth of parts (I checked RockAuto YMMV). If you attempt to recharge it yourself you'll have to rent or buy a couple hundred dollars worth of tools, and $50-100 worth of R134. Even if you just have them charge it, you'll be paying for time and labor to vacuum and leak check the system plus materials for the charge. Might be worth while to drop it off and let them do the work, but that is something you;ll have to decide.
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