The twist rate... either will work for plinking. They both stabilize all the common surplus, ball, steel cased, and standard .223 that plinkers use. The 1/7 holds the advantage for those who are wanting to go heavier for long range shooting over 300yds.
You can always mix and match parts. If you find an upper you really like, get it, and stick it on the PSA lower. Like I said, another company than PSA may offer you a compliant upper done just how you want it.
PSA offers free float handgaurds with low profile gas blocks... those are usually bayonet lug free.
Here, quoted directly from the Spikes tactical website:
NOTE: Some states and areas, like California, New York, New Jersey, Connecticut, Massachusetts require certain options and modifications. Those features can be added to your order under the Services & Tools section. Please check with your local FFL if you have questions regarding legality as we cannot be responsible for laws in every state or county.
Here are two options from Spikes:
Standard mid length upper
http://www.spikestactical.com/new/z/...fsp-p-681.html
Hammer forged barrel... good choice, but a bit more expensive than the standard upper.
http://www.spikestactical.com/new/z/...fsb-p-914.html