1 1/8 threaded headsets can be a little hard to find, I was fortunate to have a really nice Shimano DX to replace the stock headset on my Trek and then used a thread less adapter.

Picked up a Truvativ Isoflow triple 28/38/48 that has been serving me well for a lot of miles... you can change the rings on this crank set and they are not pricey. Have a nice XT crank that I need to build up at some point and could rock a 50 tooth cog on this.

Also played with a Race Face triple with a 22/32/44 and with something like this you could run a tighter spaced cassette and still have some decent low gearing with closer shifts.

Another difference between mtb and road derailleurs is their shape... road deraillers have a shallower arch and follow the line of a larger chain ring while mtb derailleurs are designed to run with a max ring of about 44 teeth and mixing these affects shifting.

Because you are rolling on 26 inch tyres a larger front ring will bring your top gear up to compare with a 700c bike.

Your bike looks great and converted mtb's make great urban assault vehicles.