Hullo Indiana, I'm glad that mold is dropping a boolit you can use, Yes these are the only 265gr.molds that Lee has produced--the RD 265.
As for sizing , you said your bore is about .430, that being the case, you don't have to resize them IMHO. They should shoot better left as cast.
How hard are you going to drive the boolits? You can shoot them without the GC with no problem. If you are going to drive them fast, they would probably be a little more accurate with a GC. But they should be ok with out.
I don't use GC's on mine at 44 mag pistol speed, mine are around 1,100fps.
I use the GC's when shooting in my marlin, but that is just me. Most folks here and on other sites don't think the GC is necessary until you get around 1700fps and higher , I think mine are around 1500-1600fps, works for me.
You don't have to reduce the charge when using without the GC, unless you are going to 1700fps or higher, then you might have a problem, who knows go shoot some loaded the way you want and see what you get, Most have found this boolit to be very accurate--Good luck , let us know what you get.