Keep in mind the 2.3 Lima to 2.5 Lima is not a direct swap as bosses on the block are different, some sensors and sensor locations are different. If you plan to use the 2.5 you will need engine bay harness and ecu. The only thing that is beneficial to your 2.3 build is the 2.5 cylinder head. Decking the head will not result in much timing change. An adjustable timing gear will aid in some performance as you can find the sweet spot at 4 degrees advanced. Note: use GATES performance/racing timing belt. Green (in color) belt seem to work best. But hard to locate.

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1999 MAZDA 2500SE, 2.5L 4-clanger, 5 speed, Green n slow. Rangers as daily drivers since 1988.
ASE Certified Mechanic, Builder of Show Destroying Protouring and Classic cars..