Hello Kevin

Here is a comparison of the 4 architectures of Firebird 2.5

http://www.iblogmanager.com/download/misc/articles/fb25_architecture_comparison.pdf

To the porting of UDF: I am using the FreeAdhocUDF from http://freeadhocudf.org/, available as 32bit and 64bit version.
May be porting is faster with this.

Good luck
Christian