The Stanley H4 lamps weren't terrific or awful, just OK. But the lamps you link are for use in left-hand traffic such as is found in Japan, Great Britain, New Zealand, and Australia. They are not safe or effective for use in right-hand traffic such as is found in Continental Europe; North, Central, and most of South America, Scandinavia, China, Taiwan, Korea, etc. What country are you driving in? And why mess with used headlamps from halfway around the world? You can get better, new, right-side-of-the-road Bosch ones from Stern, or Hellas from a bunch of vendors. I think Cibies are discontinued in that size, but I'm not sure of it.
I am in the US. Cibie seems to be discontinued in 165mm per Stern's website and now sells Bosch instead. Are H4 conversions marked for right or left side? Regular sealed beams don't seem to be so marked.
Are Hella E-codes substantially better than Nighthawk?
High beams are not "handed" with respect to traffic. Sealed beams that produce a low beam are available for left or right traffic. The RH-traffic items are marked "2A1", "2B1", "2C1", "2D1", or "2E1" depending on size, shape, and configuration. The LH-traffic equivalents either have an "X" in place of the "1" (such as "2AX", "2BX", etc.) or they have an "X" after the "1" (such as "2C1X", "2E1X", etc.). Sometimes, as in the case of the lamps you linked, that kind of code is also found on replaceable-bulb headlamp sized and shaped for direct replacement of sealed beams, but not type-approved to ECE regulations -- that is the case with the lamps you linked, which were built to conform to the old Japanese standards. Note the aiming pads and the "2EX" marking in the upper left corner of the lens.
H4 headlamps are either for RH or for LH traffic, not for both.
Whether a Hella H4 lamp is substantially better than a Night Hawk sealed beam depends on which Hella H4 lamp is being compared, and what you mean by "better".
Less glare, for sure. Also a lot less total light output and much shorter seeing distance, but a wider and more even foreground. H4 is really not a good light source for a small reflector headlamp, because it has the intrinsic inefficiency of using only a little over half the total reflector area to collect light for low beam. This is unavoidable; it is because of the shielded low beam filament which is how the low beam cutoff is formed in the H4 system. There's nothing wrong with this if you have a large enough headlamp that even half of it is still a decent enough size to collect enough light for a good strong beam pattern, but if you are starting out with a small reflector, about all you can do is meet the regulated legal minimum requirements (and sometimes not even that, depending on which regulation we're talking about). Small reflectors, especially rectangular ones, and particularly ones made out of pressed glass, present their own efficiency deficits with unshielded low beam filaments such as found in sealed beams or replaceable bulbs other than H4 (9004, 9007, H13, etc.).
If I could have any low beam headlamp in this size at all, money no object, it would be the JW Speaker LED unit. If money is an object, then it would be the Hella or Bosch H1 projector low beam in the 165mm x 100mm rectangular shape factor. If that wouldn't fit because of insufficient room behind it, and I had no choice but to pick a reflector-type headlamp, then it would be the Bosch H4 unit with good wiring and appropriate bulbs. If I needed to keep the price to a minimum, then it would be the GE Night Hawk H4666NH (the "2E1" unit meant for one-lamp-per-side systems), adapted if necessary to the slightly different socket used in two-lamp-per-side systems. But the price advantage of the Night Hawk sealed beam doesn't hold up in the long run because when it burns out -- and its life is relatively short -- you have to buy it all over again.
Yes, that's the one -- headlamp bracket modifications would be required. As far as I know you can get them directly from Speaker, but be prepared to spend money; they're very expensive. My comments about adapting were made with a 4-lamp car in mind, not your 2-lamp car.