This might helps. The IFS-R uses the 37T (53988) while the TA05 uses the 36 width pitch-18T (53935).
The IFS uses the 54045 and the standard uses the 53897
Since the pulleys are different sizes I would use the 54045 with the 37T. Also since the pulley sizes are different it affects the FDR so.... use two 37T pulleys & two belts and use the IFS internal drive ratio of 2.055 instead of the 2.25
If you don't want to buy a second belt & pulley the Internal drive ratio will end up somewhere in between.
Understand I haven't done the conversion myself but have been looking into it.
You can find both manuals here
http://www.petitrc.com/reglages/tami...TamiyaTA05.htm