Without putting it on a dyno. And not knowing the fuel type and other information. But seeing as a bws turbo setup on e-85 can net nearly 400 hp. Id say you should be right there 350 to 450 deepening on the tune and all other variables. That is a guess. I could be way off though.
Ah old school. Hahn 20G i think was comparable to like a 3147 setup ish or a small 50trim on power, more than stock wheel stage 3. Who knows with the manifold, cams, (is the head ported?) I've never been impressed with cams unless the head is ported. 425 should be doable on E85. Edit: Um, not a good idea on a stock motor, though. What's the mileage?