There's a reason no one has put a Crown Vic front end in an A-body. Yes, the swap has been around for awhile with hot rods and trucks. Typically, those applications all leave the Crown Vic suspension cradle intact. The reason for that is the crown vic cradle is aluminum. Cast aluminum. Sectioning and narrowing it is not something that the home welder should take on. Yes, it can be done, there are places that repair cast aluminum rims and motorcycle frames. But it's not an "enthusiast" level project. You should enlist an expert welder for that. As someone that has successfully TIG welded cast aluminum before, I wouldn't want to make that particular modification because of the loads involved. Obviously there's a first time for everything, but the Crown Vic suspension cradle swap has been around for a pretty long time. Long enough that guys like Denny and Gerst would have definitely had that option available to them. It wouldn't be a bad business model to take Crown Vic cradles, modify them, and sell them for use on Mopars. It would be a pretty simple gig once you had the jig set up and a welder that wanted to do it. And yet, multiple different company's have instead chosen to completely fabricate their own suspension.
Narrowing the track width will effect how the suspension handles. By narrowing the track you're decreasing the suspensions roll stability, you'll get more weight transfer during cornering. That will require stiffer springs and larger roll bars than a standard set up. The geometry remains pretty much intact, but it won't handle exactly the same as an unmodified set up.
And again, you're adding a crossmember that loads all of the suspension forces into the chassis vertically, just like the coilover conversions currently out there. The Mopar unibody chassis was not intended to be loaded that way, it carries all of its suspension loads horizontally in the K frame and torsion bar crossmember. There's very little vertical stiffness in the front end, even cars with the stock torsion bar set up have a ton of flex in the front. You would still need to significantly stiffen the front end of the car to run the Crown Vic suspension. And, how much better are the suspension numbers for the Crown Vic? Does it have better camber gain or less bump steer than a properly set up torsion bar system? Or is it just another way to convert to a rack and coilovers? Stock Crown Vic brakes are only 12", you can bolt on a set of 11.75" rotors using 73+ A or FMJ spindles and a set of the larger caliper brackets, which Dr. Diff sells for $90. If you go bigger, then you're buying an aftermarket brake kit anyway. Yeah maybe the Crown Vic aftermarket kits are a little cheaper, but you have to completely change over the suspension with significant custom modifications to even make it possible.
By the time you buy the crown vic suspension, modify the cradle, modify the A-body chassis to accept the crown vic cradle, re-work the steering column, sort out what to do for a steering rack, fabricate new engine mounts, figure out what fits for headers and oil pans (or if you'll have to go custom), and get the thing generally sorted you'll have at least as much money into it as properly setting up a torsion bar system, or buying an HDK or GST set up. Not to mention the time it will take to do all of that. Even if you did all the work yourself and came upon the Crown Vic suspension for super cheap I don't think you'd end up money ahead.
