Random thoughts:
Like just about every spotlight (I wont say all), a HID kit in Narva 225's should make them wake up.
Since Narva also sell the 225's as a HID light, the conversion from the halogens to HID should (1) work and (2) be fairly straight forward.
They utilise the H1 bulb from memory which are designed usually more for spot than spread.
As for wattage in the HID kit, I'd personally be inclined to spend a few dollars and look for either the 70 or a 100 watt kit, unless there is a personal reason why you want the lesser current draw. The 70 and 100 kits put out way more light, however, a bit more heat than the 35 & 55w HID, and similiar current draw as 100 watt halogens.
Very rough figures are:
In theory a single 100w HID ballasts + bulbs will draw the same current as 100 watt halogens (Theoretically 8 amps at 12.5 volts).
However the light output is significantly different.
100w halogen: 1500 lumens. (actual: anywhere between around 1300 to 2000. H1 measures differently to a H2, H3 etc)
100w HID: 9500 lumens, give or take a bit. (a 70w bulb is around the 7,500 lumens)
Heat issues: ignore it. A normal 130 watt halogen bulb pumped out 590 degrees centigrade, whilst I couldn't get any more than 135 degrees from a 50 watt HID bulb.
UV issues: Very early kits (up to about 2006 or so), cheap kits had bulbs with no UV light coating protection on them, meaning that after a while UV light escaping from the bulb caused deterioration of the reflective surface of the lens. Practically all bulbs these days have the 'UV cut' protection coating on the bulbs --- otherwise manufactures would or will go out of business very quick. Just something to be aware of.
If you were to find a 'slimline ballast' kit, you might just be able to squeeze the ballast inside the housing. Otherwise the ballasts will need to be mounted somewhere close by (behind the radiator grille or on the inside of the engine bay next to the radiator/headlights). You can get properly made high-tension extension wires to go between the ballast and the bulb for a few dollars (
http://www.brightlightautoparts.com" onclick="window.open(this.href);return false; or
http://www.hidspotlights.com.au/" onclick="window.open(this.href);return false;) and then mount the ballasts up on the firewall.