how much trouble to put ac back on?

There is no orifice tube in this system. There's a TXV (thermostatic expansion valve) mounted to the firewall inlet on the high side of the system, with a capillary sensing tube pushed into a tunnel on the low side line where it enters the firewall. The TXV doesn't necessarily need replaced just because the system's been left open, though it's not all that expensive and not a bad idea.

The factory compressor is efficient in terms of power consumption; its downfall is noise and vibration. Because it has only two cylinders, the torque load on the drive belt is full of peaks and valleys. If the brackets aren't put together properly or the belts aren't tensioned correctly, you can get belt slap and squeal. Likewise, because of the two cylinders, you can get pumping/line noise audible inside the car if the high-side and low-side mufflers are deleted when the lines are rehosed. An inertia-ring type compressor clutch helps out a lot with the vibration and belt noise issues; they were made for both 6-cylinder and V8 applications. The newer compressor designs actually exert more torque load on the engine because of the higher cylinder count (5 or 7 cylinders in a Sanden/Seltec compressor) but for the same reason the torque load is a great deal less peaky.

To get this system reliably up and running, you'll need to do the flush and filter-dryer replacement already mentioned, carefully inspect the hoses and replace any that look (or test) leaky or about-to-be-leaky, replace all the O-rings and gaskets. You will also want to consider throwing a new shaft seal in the compressor; they're cheap and it's easy, but if it starts leaking shortly after you charge up the system, it'll cost a lot more 'cause the system will have to be evacuated etc., new filter-dryer all over again.

You may want to consider taking the opportunity to upgrade to a parallel-flow condenser; see here. This will improve cooling performance and greatly reduce head pressure on the compressor, which in turn reduces its torque load on the engine.