You'll get a long a lot better with smaller framed thick bodied Cows to produce your grass finishing cattle. Animals fatten and marble at a percent of the cows weight and frame, unless you really want to try and produce 1300 lb. steers on grass then I'd suggest a smaller frame 1000 lb. type cow, the same goes for your bull, a forage tested bull with the genetics to marble on grass is important. Hereford and Angus produce the kind of thick bodied and easy fleshing animals that can do well on grass finishing. You'll need to time your best quality forage for when the animals are ready to fatten and marble. It's bit ridiculous to me in my area to see people advertising grass fed beef in the winter and early spring when it's been many months since high quality forages were available.
I highly recommend the Stockman Grass Farmer publication.
If you can get a farmer to grow you some grazing Corn it will produce high energy grass when grazed before it sets grain and can put on feedlot type average daily gains.