If your not planning to put larger valves and do any mods to the stock head at this time, putting 7/16" studs in it will be of no use for you at this time, especially if your going to do another head. Also, there are 1.75 roller rockers available specific for these engines, so there isn't really any need to use the 1.7 BBC rockers. Also, using the BBC 1.8 ratio on a stock, unported head will also be of no benefit for you either.
Like Hank said earlier, its going to be harder to reach the HP level you are seeking without doing some major head work and modifications to remove the restrictions that will limit you.
The 250 engine dyno tests done a few years back reached 350 HP with only 5 psi of boost, but with a big valve, lump ported head. The difference between the small valve, non-lump ported head vs. the big valve, lump ported head on the N/A combos was around 50 HP. The stock head is likely going to be more of a restriction when using forced induction than when N/A, so the power difference between the 2 heads will possibly be even greater with the ported head, and farther away from your goal than you think it might be with the stock head.
