Also, my guess is you have the 'small pattern small hole' steering arms, which is earlier 40, and some disk brake 40. There is also small pattern big hole (i.e fj60 taper), which was some later 40 and much less common, and big pattern big hole, or fj60 steering arms. I've done conversions with...
That is an aftermarket GM disk brake conversion. Most of the ones I have seen are somewhat sketchy. I would reccomend going either 76 or later FJ40 or minitruck disk brake conversion. I would highly recommend a SUMO rebuild kit, Cruiser outfitters is a great option for that. 4x/5x Series Knuckle...