Scag STT 72A - PTO CLUTCH Question

This question is for the guys that know their stuff, not the wanna bee's, please. Besides the numbers and letters, what are the main differences between the GT3.5-MC07 and the GT2.5-MC04 PTO clutch? Which one would you recommend for use on a STT 72A, and why? The clutch currently on the mower is a OGURA GT3-FE02
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Thanks in advance

Scag STT 72A - PTO CLUTCH Question