Wow, that’s a first!!
I’d probably flow another hole and see what you get.
I can see putting the new valves in, in your situation.
You have the valves and the means to do the job. It’s just some time.
If the new valves are single groove, that’s all the more reason to swap them.
I’m actually working on some 915 heads myself right now.
My least favorite part of porting factory SB iron heads is whittling down the intake guide bosses.