Be careful about buying a headset that is at or smaller than the stack height you have available. Stronglights and Campagnolos and some Shimanos are all pretty tall, in the 39-42 mm range. The Tange Levin is an excellent headset, but there are more than one model/stack height that are/were sold as Tange Levin. The one with plain rounded outer races is fairly short 33-34, while the one that's a Campy knock-off, with annular groove in each of the outer races and engraved lettering in the groove is more like the Campy stack --39.5 or so.

You measure stack capacity by measuring the headtube (frame only, excluding any headset parts), and then measuring the distance from fork lower headset race seat (where the pressed-on race sits) to the top of the steerer tube. The difference between them is the stack height. You can always shim up a too-short headset, but you can't shim down one that's too tall.

On the bottom bracket, the Tange/IRD sealed bearing units are nice, and inexpensive, available in several lengths. Need a 20-tooth ISIS socket to install them. They have JIS squares, which should fit your 105 crank. Soma sells two types, the lighter, more expensive, hollow axle one, and the standard, cheaper one; I assume that the bearings are the same. They're also available on eBay, for less money. Velo Orange sells a JIS BB too, either the Tange or a Shimano unit, their choice apparently (whatever's on the shelf).