The Weber AlNiCo will fit without the shielding around the magnet. You could consider the Eminence Legend 10516 as a speaker choice also. The output transformer impedance is really 16 ohms so you may want to get a 16 ohm speaker. On the tone control if you remove C5 and C4 and change C1 to 470nF then the tone control will be set to bass at CCW and treble at full CW. The op amp used to boost the treble so to make up for that changing the first triode bypass cap to 470nF will make up for not having the op amp boost.