Hi
You are looking at proper Part Number.
The 98AG is year/model info
The 15X801 is general part description for remote
The AC is design level.
Do not buy anything else apart from level AC or later (ie.. AC, AD, AE, AF, etc) The second letter here is specifying mods, improvements, etc. They will replace earlier levels usually. Only a dealer can confirm by checking the replacement chain. Levels starting B_ or C_ or D_ will not work unless Ford specify in a Service Bulletin or instruction from engineering. The number you see is probably part of Finis number (7 numbers) Dealers use these, but they relate nothing about design. So try to get a AC level or check with dealer for replacement numbers.