As others have said, this isn't purely type related...a lot of this is personal. However, I believe it is at least somewhat type related.
And not just on the SF level, but on the ISJ level. ISJ's have dominant Si, so we like consistency and stability. His whole "this is the way we've always done it" thing is pretty typical for an ISFJ, particularly an older one. Some are more adventurous than others, but it's generally true.
I think the biggest thing is that taking risks involving sudden change can be tough for an ISFJ...it's leaving the safety of the known. It's hard to try a new idea because one is always fearful that the new idea may make things even worse than they already are.
Unfortunately, I don't have much advice in this situation, since he's "not good with numbers". If he can't understand the concrete information, then it will be hard for him to take on a new approach. He would have to be very clearly convinced that continuing his way will doom the company, and the only option of saving it is this drastic change.
It can be tough to get an ISFJ to change. For me, I really have to feel confident that the change will be good.
It also may help if you can get a lot of people on board with your ideas. If it's just a few of you, then he may not take you as seriously. But as someone with Fe, if he feels like lots and lots of people in the company agree with you and your supervisor, and you're all united in believing this new approach will better, then he'd probably be more apt to listen...he wouldn't want to make a decision that the majority of people in his company disagree with unless he felt very strongly that his way was definitely right.