Called a Vespa dealer to confirm a different part# between the 300 shock and that of the 200/250 (same).
Was very pleased that the price (~$160) was not shocking.
Anyone look into this for mount compatibility. Figure my next step is to eyeball and take the leap.
I'm hoping the newer shcok will perform better. Expect it will have a stiffer spring, but hope it will have improved damping, which seems to be the shortcoming on my stock shock (06 GT200, which apparently has an improved shock over earlier models)