Measure the length of the steartube and the length of the headtube, what's the difference? A GS headset should be close to 34mm... you may need a couple spacers between the adjustable top cup and the locknut.

As for the hub... if the frame came with a six speed I guess it might be 126mm spacing... you can measure with a ruler.. is it? Calipers and removal of the freewheel would be ideal for measuring the over locknut dimension of the hub but you could also pop it in the dropouts without the QR in and butt it up against one dropout and measure from the space between the locknut and the dropout on the otherside if there is indeed any difference. You may have a 120mm hub in which case it would not hurt to swap out the axle for a slightly longer one and some wider spacers. forcing the stays in 3mm on either side isn't a huge deal, i don't believe anything would come of it, but it is not ideal.