With either rack loaded with dishes and pulled out, a machine intended to be built in will definitely tip forward without being fastened to something like a counter or a substantial housing.

To make a build-in model into a portable, I don't know how one would calculate a counterweight when the weight of loaded racks can vary depending on their contents.  I think the butcher block tops of portable models serve as counterweights, but there may be more to ensuring their stability than just that.

I have a number of BI machines I turned into portables.  I built simple carts, put wheels on and made sure the cart extended a few inches extra in front.  That solved the tipping problem for me.  I can have both racks fully loaded and fully extended and no tipping.  Sorry the picture isn't the best but I have them in storage in the shed and it was hard to get a good angle to take the picture.  I wish I could photo the entire cart for you.  I had the wood cut at Home Depot.  I glued them an reinforced them with screws.  I remove the feet altogether from the frame and screw the frame to the wood cart.  Very simple and works perfectly.