Do you have a specific question? As long as the PSA upper and the S&W lower are both within spec, they will work together. Have not done it with PSA, but I have put a CMMG upper on a S&W lower, and vise versa. Also have a rifle with a BCM upper on a Spikes Tactical lower.
I have been looking at the complete upper from PSA.
PSA 20" Rifle Length 5.56 NATO 1/7 Nitride 15" M-Lok Upper with BCG, CH, & MBUS Sight Set - or one of their other 20 inch uppers.
Or change out the handguard to AR15 ATLAS S-ONE M-LOK Handguard or something similar. I would also have to change the gas block and buy the tools to do the work or have it done. Looking the the cost it comes very close if not more than a complete upper.
Last month I bought a PSA kit and a Anderson lower, a mag and sling and put it together for less than $350.00, minus the carry handle which I already had. It works fine, and works just as well on my Bushmaster and DPMS lowers. It should work fine on a S&W lower.
I put a PSA upper on mine and love it 18 inch rifle length gas system 1 in 7 twist barrel with a Wylde chamber, it shoots MOA with Hornady 75 grain match ammo.