My first thought on reading your request was " Why does he want to stack adapters, there has to be a neater solution?". Are you just looking at the front part of the housing (to engine) or is the second part you refer to the back part of the housing (to transmission)? Dimensions of the mating surface of the 2 parts for different SAE housings are given at
http://powerlinecomponents.com/liter...heel_chart.htm among others. I think the SAE standard must also make some kind of reference to the fore-and-aft location of the split in the housing as it doesn't make a lot of sense to define a standard for interchanges that addresses diameter but not length. The full set of SAE standards took up several feet of shelf space 30 years ago and must be bigger now, have a look in University libraries (School of Mechanical Engineering).
A quick Google on "cummins sae 3 adapter" gave just short of 3 million hits.
It seems others are looking at the same puzzle
http://www.cumminsforum.com/forum/cu...3-adapter.html
One of the hits was
http://www.ebay.com/itm/Cummins-5-9-...-/121187222191 The search also came up with several hits for SAE 2 housings if you do want to go that route, for example
http://www.ebay.com/itm/Cummins-6bt-...-/130993277141
Another Google on "Cummins 3903282" confirms the part number in the ad is a Cummins part number
http://www.forengine.com/parts/Cummi...-Flywheel.html These folks also list other housings for the 5.9 with different positioning of the starter and mounting points which suggests you might be well off having a chat with your local Cummins shop to see what's what.