What sort of reflector is it?
If it's a CFL reflector (mirror finish) then a 1kw bulb will not go well with it because you'll get hotspots. If it has an embossed finish that'll help, but it'll need to be an open-ended reflector because a kw bulb generates a lot of heat.
Generally speaking I'd only recommend using rated hoods for bulbs.. and the higher wattage bulb the more that principal applies. I have a 250w DS bulb in a powerplant CFL reflector, but that works fine. It's JUST about ok with a 400w MH bulb in it, but anything higher than that and it'll toast it I reckon.
What you really don't want is a fire, so cut corners very very carefully.