1994 Chevy S-10 Recharging air conditioner unit

Very easy, id say easier then inflating the tires.

First step is to buy a do it yourself kit, locate the large diameter hose that goes from the ac pump to the dashboard.

Then start vehicle and set max ac, max fan speed, and max cool, remove the cap off of the hose, attach hose and check reading.

Then shake up can and tilt 12 oclock then 3 oclock every few seconds untill pressure is at 35, or blue.

It depends on what that vehicle has for a compressor and what the system was put together from. Being a V-8 conversion what compressor did you use? If it's the original one from the 4.3? Check it for the type and amount of refrigerant. Also does it work at all or not? If not your better off having the system leak tested and recharged after any leaks are repaired.

High and low pressure ports should be the same irregardless. Probably just wants to top it off, good to do that lets the engine run more smoothly.

Unless it has an R-12 system. 94 was the year of change for the S series. The later P/us were R134a but some of the early built units and all the S Blazers were still R12. In 94 the S series went all R134a for domestic sales. Makes it fun sometimes. On the car side it is even more fun since some models were R134a in 93 while others didn't convert until late 95 for the 96 year.
So it depends on what they used to put the V8 in with. If the OPs lucky it will be an r134a system.
Also keep in mind that "topping off" is not legal in many states and quite a few countries as well.