As Eagle numbers were relatively small, you'll likely find a lot more upgrades were done on the 258 in other vehicles, like Jeeps. Jeep forums are likely your best bet. Google.
What I would question is what is the goal of your upgrades. Are you just upgrading what you can because you can, or do you have a hp, torque or curve that you expect to get out of it for on-road or off-road. Is this your end target or a step on the way to a stroker.
One of the things I've seen mentioned a lot, is people putting a carb on that has too much flow, giving them little more performance, sometimes not running well, and costing a lot more in fuel at lower rpm. And at some point, you'll need to widen the exhaust: the air can't get in fast enough, if the air inside can't get out fast enough. One rule of thumb I was given for head/cam/carb upgrades was go to 2.25" exhaust for most upgrades, with 2.5" being of no or questionable benefit due to the limits of the engine.