A standard SPI engine has about 63 bhp.
If you were to fit a 266 cam, your twin HS2's, a gas-flowed head with 35.66 inlet and 29.5 ex. valves and a CR of c.10:1, plus a better exhaust manifold and exhaust system you could confidently expect around 75 to 80 bhp and it would drive really nicely.
For better acceleration you could use a 3.44:1 FDR and it would cruise at 16.5 mph/1000 rpm in top.
