Old dogs do have problems learning new tricks. You might find a small injector body on Ebay, but in the 1000cc motors we use like a 45-48 mm throttle plate, they are a little harder to find. if you don't have any money.

The new electronics are almost fool-prof kinda of like your computer, if it messes up unplug it plug it back in and it is usually fixed.

To tune with electronics we use an old clayton dyno to load the car down. We used to use a road with a hill in front of our house but the Sheriff said he would rather we did not do that.

It is a good idea to have an air fuel meter to ck your exhaust gasses.
You set there at the computer have a helper bring the car up to the speed you want to adjust, read the meter go to the cell you are working on and type in a number larger or smaller than the number you are adjusting, check it and if the number is right the ex gas will show it and you go to the next cell. Sounds complicated but really simpler than sitting here trying to type and spell these words. When you are done about 30 to 45 min. The injector is spot on for every rpm and load you will see at the race track. We adjust for every 1000 rpm some anal type do it for every 500 or even 250 rpm's. with mechanical you have low speed mid range and high speed that you change. When the sun goes down you change pills. We have a little sensor that sniffs the air pres. and changes the settings as required. we run good at sea level in the sun or a 3000 feet in the snow.

It aint rocket science.