> It'd probably have to be touched up a bit.

This may be an understatement. :-)

In the first 50 lines of the 3897-line dtoa.c file, I see this warning:

/* On a machine with IEEE extended-precision registers, it is
 * necessary to specify double-precision (53-bit) rounding precision
 * before invoking strtod or dtoa.  [...] */

It seems to me that figuring out how and when to do this, and
writing and testing the appropriate configure/pyport/whatever
code, is already a nontrivial task.