Main caps should have a interference, press in tight fit, not drop in and fallout.
The factory align hone the blocks with the original main caps to make the main bearing fit properly, if your caps are loose you need to have that fix with either having a good competent machine shop fix yours or buy new after market main caps (I use the aluminum ones from 440 Source , do not use steel ones form any maker ) and have them fitted and align hone to your block
You may need a shorter timing set also depending on how much the shop removes from your main saddle align honing it