What bodies can i use on this? i would like to run a gp38 or 40 body if possible

A street car body or a very small 0/6/0 or 0/4/0. I used a dock side and it worked very well. Very little modification. Adding MTL couplers is a problem. I used dummy knuckles.

Is the Kato 11-105 driven on one truck or two

Electrical pick up seems to be both trucks, but only one truck drives the train.

Re: Kato motorized chasses 11-103 through 11-107, which is more powerful? also shortest vs. longest? where bodies available? Thanks.

Hi , it is different of these unit number to be installed the power unit . So , it is not the powerful , but the type to be the making trains . The 11-103 is used to light , small trains , for example B trains shorty . In N Scale , it needs not to be the powerful . I think , It is difficult to be changed from the train of 11-103 to the unit of 11-107. The speed is from power pack .

What are the dimensions, Length,width, height. & truck spacing ?

58mm long x 15.3 mm wide . 32 mm center to center of the trucks . 15.9 mm high , if you search this on a popular online auction site they show pictures of it with the measurements . you'll probably need to look at several listings to find the seller that shows pictures . when I purchased several of these here Amazon had the best price