Thanks for your feedback.
I cut some bolts to size, ended up with 65mm and 60mm length bolts for my deeptuttle fins.
I do wonder why my 121 was supplied with tuttle bolts only (70 and 80mm). It would make sense to supply deeptuttle bolts too, the 121 after all has a dt finbox. And add the deeptuttle sizes to the fin bolt chart?