The following pretty well hits the points except for not having the interleague games all that concentrated toward the middle of the season. Pairing them and playing them early week somewhat scattered allowed for keeping the traditional baseball week. And it made for fairly evenly spread-out offdays, though not with one every week.
If you really had you heart set on piling the interleague in the middle of the season, that can be done. There would be other choices to make too:
- How concentrated, like all interleague in a row within a month, or not quite all consecutive?
- Okay with having an offday for each team every single week? The alternative would be scattering the offdays but not adhering to the tradition Mon-Sun week with two series (or three when there is interleague play).
There was nothing about start date, but that can easily be changed from beginning of April as I set.