Upgrade from 32-bit to AMD-64?

[Karl Denninger]

I have a machine that can run either (proved, I can boot the AMD-64 
release disk)

Can I SOURCE UPGRADE from one to the other?  That is, is it possible to 
do a "make buildworld", "make buildkernel" and then "make installkernel" 
and wind up with AMD64 instead of the 32-bit code?

Or must I reinstall?

It APPEARS I can run most 32-bit code on a 64-bit system.  Not all 
works, but most does.

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Karl Denninger
karl at denninger.net