I would suggest that you make your longbow one that is tuned and tillered to be shot in a way that is similar to the same way that you shoot your recurve.
What I mean is this, traditional longbows are set-up to be shot with more palm into the grip, similar to the way you would grab a broom handle in a vertical position.
There are a lot of longbows out there designed to be shot by just gripping the bow around the throat of the grip, in the same fashion as many of us shoot recurves.
Like the Tomahawk mentioned above, it does not have a radical departure from the design most thought of when one looks at a traditional straight longbow grip.
I have been in this game for over forty years, we have never had it so good as we do now. There are so many good, shootable bows out there of every type of design. They shoot harder, faster, and are more durable then ever before.
I would opt for one that has a lot of center shot, older longbows and recurves designed with the same grip are often shot off the side of the bow.
It is truly a great time to be a traditional bowhunter.