I understand that you want to make him a C, but let's say here were to face an opposing C or PF that could shoot jump shots and threes. As a result of his atrocious OD, he might get torched. The same thing could happen if he happened to make a defensive switch with a teammate. If he was to make a defensive switch, he would need some OD to defend a guard, should the situation arise.
Another reason why I recommend training OD is that it is a cheap skill to train for C and PF, and it is worth the salary cost. Since you are in D5 Italia, you might be able to train him freely, if there is little to no competition.