$75 for fitting is a deal.
Shipping is a factor.
Fitting CPA triggers to an original 44 1/2 is a time consuming and frustrating chore. After the 3rd or 4th one you probably get a system down.
Unless you already have a suitable lever installed, it’s two jobs. both require some fitting.
You also need to make sure that there is a hammer fly installed and that it is not upside down. Most single triggers have one, unless some one found it on the floor after a deep clean on the rifle and had no idea what it was. Second choice is not knowing how it went in and installing it upside down and backwards. Since it has no function in a single trigger, you would never miss it.
The trigger is probably best fitted by stripping everything out of the rail that is the bottom tang. There is a good chance that the height of that rail will be too high for the screws that hold the tang into the action to line up. Unless you are really careful, it might cost you a sear. Filing down the offending part. The other option is to work on the action.
Once you get the lower tang installed and flush with the action, the two rear screws holding the tang, determine everything else. They can’t be moved. The forward screw, passes through, and may not line up. A bit of an oblong hole here doesn’t seem to hurt anything.
Then the front of the tang needs to be checked, a good chance that it is long and is no time flush with its mating surface area. This is more than cosmetic. The more forward the tang sits, the more likely the link will hit it and not allow the lever to open all the way and the extractor may not work correctly, or brass may not clear the breech block with a large case like the 32-40.
Once the lower tang fits the action, reassemble it. Install and check function, with screws tightened. If the rails on the tang fit too tight into the action, it can cause enough pressure to squeeze the trigger parts. Enough that the sear will not move and catch the hammer. Or just enough that the set trigger will not set. You need to remove material from the rails. Or modify the action to a point where the original trigger should just be thrown away, because it no longer fits.
Once the trigger fits and works, it’s time to install or check the lever. The rails on the CPA tang are thicker. This interferes with the link. One or the other needs to be modified so the lever drops all the way.
I might have forgotten a challenge or two, but those are the high points. Plan an afternoon.