If you're looking for more American, I'd just stick with a classic American ale strain (1056, WP001, US-05, etc.) and ferment at a low temp (65ish). Most of the hefeweizen yeasts are going to produce some levels of esters/phenols, and if you're looking to avoid that I'd just leave that out of the equation. The American ale yeasts will let the wheat shine through so long as you can keep them cool enough.