OK, I think I have some information for you.
First up, here's a link to a measurements chart at Parabox that details all the measurements of the standard bodies. Large bust not included.
Obitsu Body ChartSecond, here's a link to a doll measurements chart that includes the Tonner AM
Doll SizesMariko has the Parabox large bust, and is actually on an Obitsu 'soft body A' which is a little thicker than the standard Obitsu 60cm body that you get with the ball-jointed Obitsu 60. I have some pictures showing her in comparison with Dianna a Tonner American Model (she's originally called Belle Grande). There is some nudity in the pictures so you can clearly see the body comparisons. I also swapped their outfits to give you a practical demonstration of how things work. Amazingly, I don't have an original Tonner outfit, however I do have a OOAK gown made specifically for the American Model that Diana is wearing. The dressmaker that made it hand cut the lace bodice and formed it on an American Model body, so it is specifically fitted for an AM.
The large bust piece that Mariko has has a bust size of 28cm (10 3/4 inches) and an under the bust measurement of 22cm (8 3/4 inches).
Here are the pictures (Nude dollieh alert! Nude dolliehs!), I think they explain it better than I can with words.
Here are Mariko and Diana side by side in their outfits.
Here's Mariko;
Here's Diana;
Here I undressed the girls and did some side by side body comparisons. I've put them together in a large image that you can expand. The smaller image in the bottom right side has some lines on it, the idea is to show the relative positions of some pf the body elements. The Blue lines are the Tonner's and the red lines are the Obitsu. The Tonner has a longer trunk and neck, and so has a much longer body than the Obitsu. The height difference between them is all down to the lovely legs on the Obitsu.
Now I've swapped the outfits, and Mariko is wearing Diana's lace bodice gown. She looks pretty darned good in it.
However there are some compromises. The shorter neck and higher breasts of the Obitso mean that Mariko can't quite fill out the gown the same way, I took a couple of closeup's to show what I mean.
Finally, here's Diana wearing Mariko's outfit, the keen eyed reader might spot that this is actually a Volks outfit for a DDdy, but fit's Mariko rather well. Diana thinks it fits her well too, but I think she needs a push up bra to help.
So, there you have it. I think that most clothes (except pants) that fit an AM will fit an Obitsu 60 body. The smaller bust is compensated for by the overall size of the chest. So things fit the bust. The trunk will need to be a little shorter and the waist on the AM is lower than for an Obitsu. But the big difference will be in any kind of pants because of the Obitu's incredibly long legs.