They give OG, so divide that by the potential extract of the grist and your efficiency to get the total grist weight, then keep the malts proportionate.
For example, at 65% efficiency: 13.2°P * 3 gal / (9.2 °P-gal/lb * 65%) = 6.62 lb
C40: 6.62*50/528 = 0.63 lb
For hops, it's a 10 bbl recipe, so divide by 110, give or take. Without knowing AA% that's the best you can do.