for the trigger, finding a short on may be difficult. To fit it all you need to do is shave the sides of the trigger, and trigger bow until it moves smoothly in the grove. Setting the trigger reset screw is a bit of trial and error
The mainspring housing should be basically drop in, but remember there are 3 parts inside the MSH and the retaining pin holding them in. after those parts are replaced in the new housing all you need to do is a little hand fitting.
10-15 mins of work