as I did. littlemachineshop.com carries the complete kit:
bed, lead screw, rack, ship pan, motor pivot mount conversion.

The actual tailstock to spindle distance will be closer to 18".

Simply no comparacing to the cramped quarters of
7x10. Price vise - starting off with 7x10 and upgrading
later will cost about the same as going with 7x14 outright.

So - if you're just starting and are not sure if the hobby
will last, 7x10 is still a viable start.