I had the same question about my .45-70 handi. I wanted to use Hodgdon's Varget and did not know which level was safe. I called Hodgdon and asked about using Varget in the handirifle. The technician told me not to worry about it. I could use the the heaviest data for it.
Also, there are a couple of companies that make super hot, factory loaded ammo for the .45-70. They include a list of rifles that are safe for this ammo. The handi is included on their recommended list.