Originally Posted by S&W Rover

Upgrades consist of:

• Apex Spring Kit and Trigger
• Steel recoil spring assembly (read the thread on this before doing it!)
• Improved (wider) takedown plate from Galloway or NDZ
• A wide array of sights (i.e., sights that fit the M&P also fit the SD-series)
• Talon grip panels
• Two slides available -- black or silver-colored stainless steel

Am I missing anything?

I don't think there is a threaded barrel or a custom barrel for the SD, such as those made by Lone Wolf, Storm Lake, Apex, etc., for M&Ps.

As noted by others in this thread, aftermarket parts for the SD-series are few, compared to Glocks and M&Ps!