question about location and type of drain for a rectangular ofuro bathtub

Please note:
1) We cannot install pop-up drain fittings.
Basically, there are no standard fittings for a thick bottom plank such as a wooden bath.
Even if we were to modify a socket and adapt it, we could not be responsible for mechanical problems, spare parts etc. so we prefer to stick to a rubber plug type.
If you prefer, we also have a spherical shape available.
http://www.bartokdesign.com/japan/0-blog_news/spherical_drain_plug_1.php

2) Yes, we can place the drain on one side, please note that we recommend an offset of 55mm from the internal wall face.
On the other hand, if you are planning to attach the drain to the plumbing using an elbow, the "feet" under the tub will interfere with it. If you let us know the direction in which the elbow will be pointing, we will calculate the offset and place the drain accordingly.