This is called the s15g system by the folks who used to be at MCFA when this truck was new, and in spite of what swoop keeps calling 'tier 1', this is the tier 1 MCFA product, and was made/sold in 2003 only.
"dwell" on this machine refers to the fuel trim solenoid valve (red and white wires, sticking up on the thing mounted beside the LPG regulator), and while it is good to be able to see for some troubleshooting, is not really something to be adjusted. What is the symptom you are trying to fix? [?who told you to try for a dwell setting?]
The controls on this machine are not good for idling more than about 4 min with out getting the MIL light on. and the main adjustment made with the laptop is the accel pot.
The hook up of the vac lines can sometimes be confusing, and cause problems. there is what looks like a "tee" that is not a "tee" and miss connection of the lines can cause it to run bad, Some early units had an elbow that had a 'bb' sized ball inside on the vac hose right at the metal section of the large air intake line over the valve cover, that can get stuck and cause intermittent shutoff or rough running.
NEVER test the red and white wires on the fuel trim control valve with a meter or test light, you may well let the smoke out of the little black box with next key cycle, and is a pulsed signal.
Does this unit's little computer box have only white potting that you see when you look into the hole where you plug the computer? if so you will need to insure the vac hose is what appears to be unreasonably long. if you can see transistors rather than just plastic, the vac line connection is a plug and does not require a particular length hose. the engineers used the hose length to calibrate a vac drop, and lots of folks looked at the hose and said it must be too long, so they shortened it. Barber Coleman made the original system, which had been in use for years on stationary power systems for air compressors, but as they run at 1 speed and load most of the time, there were some problems with operations that the operator had a clamp and "bounced" control handle more than 3 times to hydraulic stall while driving, and Barber Coleman went out of business, so the computer had to be redesigned and sourced from a different vendor. The vac hose on ones with the white plastic potting should be the lowest hanging point on the truck.
As this unit has only a 1 wire O2 sensor (not heated) this truck does not go into "closed loop" until the engine is at normal operational temp, and the temp sensor to the controller is not the same temp sensor as the dash gauge sees, but is 2 black wires on a lug mounted to one of the manifold studs, and may be confused with a ground lead.
btw, if this truck had the correct carb, you would have a plug and not a screw to set.
I would also note that on this truck one of the more common missed connections is on the throttle body, where there are 2 vac line connections, make sure the one closer to the engine goes to the computer, the one further away from the manifold is where the connection to the distributor vac advance goes.