The standard #1 Indian 303 will work, (a friend has one and we tried it) but the original is closer to a Speed magazine from what I am told. I was told it was a 7 round mag.
I have never even seen one other than some pictures I have saved.

I am ready to compromise and use a #1 mag so I can get the project started. Then I will change it to a 7 round or even a smaller one lat3er if ever I can find one
Do you have any #1 magazines?
If you'd like I can send you pics of the rifle I have. Please PM me and give me your personal e-mail address and I'll send pics.