Your best bet is to Google old metal halide reef threads. Pendant shoot-outs ect, that will narrow down what you should be searching for used. That is in regards to what will light your footprint best and at what mounting height.
Anything metal halide that's not reef intended should be avoided. They will be spotlights and heat monsters. I worked specifically on commercial and industrial lighting (converting MH and fluorescent to LED) and believe me you don't want those over your tank. Event the ballasts will burn the heck out of you. I've come across ballasts/fixtures that were posted earlier in this thread dripping nasty black goo and still functioning. Don't want that over your tank.
Keywords to search FS threads as well as craigslist, FB marketplace, offerup ect.
Some manufacturer/pendants names. * implies fixtures I've ran, that run cool. As in can touch the housing with no risk of burning. I would look for pendants that are whole, with the aluminum housing not just bare reflectors.
*Hamilton Technology ; Bali Sun, Cozumel Sun, Cayman Sun and some others that are t5 combo
Lumen Bright mini and large pendants
LumenMax Elite and Large pendants
*Reefbrite
Giesemann but the pendants are smaller and they are expensive. Spectras are mogul with t5.
Ballasts to search:
Lumatek
Galaxy
Reefbrite
IceCap
Coralvue Luxcore
First step is decide if you want single ended (mogul e39) or double ended (HQI). This will dictate what pendant you're looking for as well as what ballast to pair it with. I always try to buy selectable watt ballasts that go from 250w-440w. A very shallow tank or smaller tank I'd do the same with 175-250w. This will also include the wattage you need for HQI lamps but let's you start lower wattage and go up from there if need be. I choose mogul ended setups because I feel at this point there are more bulb options still around. HQI seem harder to come by. Also easier to install and swap without breaking.
From my pendant list above, I would narrow a suggestion down to Reefbrite or Hamilton Tech. This is based of my experience with them having best spread and them run surprisingly cool. The ballasts I would narrow it down to would be Reefbrite or IceCap electronic ballasts. Reefbrite ballast with a Reefbrite pendant is as plug and play as you can get. I've ran Radium 250w, Hamilton 250w and Reefbrite 250w with them. All fired fine and looked good. Radium, slightly blue and under driven. IceCap gets a feather in the cap for selectable e-ballast. You can choose to overdrive at 250w HQI, allowing you to run HQI lamps or get the Radium lamp closer to what they are meant to look like. That said, hamilton lamps are awesome IMO. The other ballast choices are good too but will be used and more than likely no guess on how many hours. That said I'm running 1 lumatek selectable and 1 galaxy and my 400w 14k Hamiltons look the same to the eye @ 400w setting on both.