The 250 heavy duty was used to differentiate it from the '97 f-250 light duty that looked like a '97 150. It is still just a 250. There are a few differences between 250 and 350, like the frame, number of leaves, etc. The 250's are easy to swap to straight axle, so if you find the right truck, don't let the TTb front throw you off. Just plan on spending $1000 to $2000 to put a solid D60 in it.