I have installed the trigger guard and the front and rear trunnions are being held in place by C-clamps with patches to pad the receiver.

Magazines lock up front to rear with little to no play, but there is some play side to side in that I can hold the bottom of the mag and move it. I installed the bolt and recoil spring and that lessened it but there is still a little left.

Is this cause for concern?

nope ,build it up
have checked out how much slop and play that there is in a wasr-10
if you have one you prob wouldnt be worried about it

BLM

That is normal.....Some are tight and others are  like yours.....

the have to make it alittle big
because some mags are bigger then others
and if a small mag was tight a thicker mag wouldnt fit