Is that considered an SBR even though it's in pistol caliber ?
Also , is the mag well set up to use pistol mags or did it need modified ?
Yes in this configuration it would be considered a SBR. The upper has a 6" barrel on it. Caliber doesn't matter.
Using the Olympic Magazines no lower modifications are needed. Thats one of the reasons I went with them. My lower is a registered M16 and I wanted to shoot it in FA, otherwise I would have gone with one of the AR45 lowers out there.