A very old 2N2907 was in an old metal case. The PN2907 has the same chip but it is in a newer plastic case.
I di not know what "403" is for, it might be a selected hFE.
Derek, as a learning exercise you should get data sheet for 2907 and BC327 and compare specs and see why they would be compatible. Then in the future you would be able to find a substitute on your own
What the heck, here is snippits from the data sheets.
Although there are thousands of different transistor designations, there are, in fact only, a few categories of transistor. Sometimes different part numberd transistors have identical chips inside. There are a few more words about this @ https://www.electro-tech-online.com/articles/core-components.782/
But, if the transistor is for some specialist application, particularly high frequency, you need to be much more careful with substitutes.