No you can't do that. suntour and shimano have different spacings between cogs and the cogs are different thickness. also the distance the RD travels on each shift is different aswell.
you can use your shifters on friction mode and that will work for almost 9 speeds.
you might be able to use those wheels and replace you Suntour 6spd shifters with a pair of shimano 7spd ones and that may work.
great looking bike BTW, you do have the model with the Suntour Sprint right? the Blaze on was OK but not nearly as nice as this one.
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“One morning you wake up, the girl is gone, the bikes are gone, all that's left behind is a pair of old tires and a tube of tubular glue, all squeezed out"
Sugar "Kane" Kowalczyk