I suggest you read my build thread. I have what might be the fastest OM617 in North America (though there may be someone quicker out there) as proven by actual timing slips from a real certified set of clocks. Just to let you know that I actually know something.

EDIT: Link to my build thread: I'm Back! S-10 OM617 Project You can skip to at least page 5 or so and not miss anything.

With the mods as detailed in my build I have right at 223 HP (IIRC) rear wheel measured with a DynoJet so that's probably a bit high. My point is that your OM617 goals are pretty ambitious but I'm not saying you can't get there. My current HP readings are with a SuperPump and a stock turbo with clipped vanes. I have a big turbo ready to go on but haven't had time to mess with it yet.

Be aware that these engines are not cheap to build. There is little off-the-shelf stuff for them so you have to be prepared to make a lot of your own bits and pieces. If you're paying someone to do this for you it's going to be pricey.

I know nothing about the 606 but it might be a good choice. I didn't consider it as it's too big (displacement) for my class rules and probably wouldn't fit in the S-10. I barely got the 617 in there!

Interesting project

Dan