Re: My second build..Thanks to all of you.
Phat, glad you've gotten this far and your problems are minor. The coaster brake arm can be bent cold. No need to purchase a torch. It just requires a 'Z' bend, just enough to clear the sprocket fasteners. If you have access to bench vice that's all that's needed.
1/4" is a little much. If you can reduce that by half you should be good. The closer you can get to perfect alignment is best.
As for the chain hitting the chain guard; my guess is the chain is too loose or the guard is mounted too close to the chain. There should be some adjustment room there. Look at how the guard is mounted at the rear and simply raise it a little. I personally run a chain guard on all my bikes for safety and for looks. Some need to be trimmed in places and mounted well.
Pedaling with the clutch disengaged will allow some slack in the upper chain run and I assume that's where the chain is hitting.
As for the chain tensioner you must remember that it is intended to be a 'tensioner'. Not a guide. Once the chain and sprockets are aligned the tensioner is there only to allow adjustment in chain tension. It should not 'drag' the chain to either side but be centered so that the wheel rides centered on the chain. That often requires a slight bend or twist in the tensioner bracket to get the wheel to align with the chain path.
Age and Treachery Will Always Triumph
Over Youth and Skill & "Charlie Don't Ride"