Newbie home length question

How many used homes have box lengths outside of the standard 56’, 66’, and 76’?

I’m reconfiguring lots in my park, and pouring concrete on several pads to extend them. On a lot that I have, say a 72’ length available, I’m trying to decide how far to extend the pad back: 66’, 70’ or the full 72’. Any recommendations? It seems like most homes would only be 66’ long, so the extra concrete is just a waste of money. Are there a fair number of homes that have an actual box size of 70’?

I tried browsing used home listings, but it’s hard to tell if the length listed is the actual box length or not.

Are you buying and bringing in the homes yourself or are you advertising for owners to bring in their own home. Either way why pour concrete before you know what home is coming in. Is the demand so high that you expect them to arrive daily.

This is my first time doing concrete pours, but it seems easier and more economical to reconfigure several lots at once than one at a time. There seems to be a shortage of concrete contractors in my area, and many are booked several weeks out, and concrete work has to be planned far in advance.

I am doing pours to move homes in myself.

Does your building code allow you to simply add piers as required to support the home beyond the existing pad. That would be a very simple diy solution.
Park the home on the pad and add piers yourself as needed.