The FD-6603 is really designed to be mated with a 52/39/30 crankset with an intended difference of 13t between the large and middle chainrings. I am currently using this same FD with a 5603 crankset (50/39/30); the smaller difference between the large and middle rings means my FD must be positioned a few mm higher in order for the back of the derailleur cage to clear the middle ring. Though indexed shifting has been excellent with this arrangement, and I've never dropped a chain, I believe I am at the maximum tolerance for this FD. I would think a 48/36/26 Sugino crankset would have a better chance of working with the FD6603, but it's still not ideal due to the cage being shaped for larger rings.

I haven't heard of anyone successfully combining a Shimano GS RD with a 34t large cog, though I understand some people are able to exceed Shimano's recommended 27t max a bit...dependent upon the design of the frame's RD hanger. Additionally, the long cage road derailleur isn't designed to handle the amount of chain required for your chosen gearing.

What shifters will you be using. If you're using barcons or downtube shifters, you could use a Deore or other MTB which would work fine with your chosen crankset. For RD, I'd go with a long cage (SGS) MTB model, too.