Your PS pump is a Type II, w/either a .750" or .660" shaft. (The Type I has an integral steel tank.)
There is a 5" pulley. It is for a .750" shaft. Part number is 10166335, goes for about $40.00 new.
Summit sells a nice aluminum reservoirs, p/n 340202, but it's steep @ $81.00. Nice hose, fittings and the 16 mm to AN -6 (Summit p/n 991955, $6.25), etc. is another $50.00, give or take.
The above info is in part from the May Car Craft.
The idea of a hidden tank is a good one, IMO- I'd opt for that, personally. BTW, a truck and F-body alternators appear to interchange.