I agree with the others, you will gain the most accuracy with a good hard fit barrel (hard fit means tight at both ends).
In the 1911 platform 80 percent of the mechanical accuraccy is the barrel and the fit of the barrel.
The only time I would consider tightening the slide to frame would be to correct the functioning of the gun, in most guns this will not be needed.
That being said if you are going to tighten the slide to frame there's only two ways I recommend it be done. You can weld up the frame rails and then machine them on a milling machine or have Accu-Rails installed in the frame, I prefer the weld method.
I seen more then one frame and slide ruined by the old squeeze and peen methods.
Regards
Bob Hunter
www.huntercustoms.com