So far the not so helpful AI generated answer is to use a 38-70 sizing die after anealing a 45-90 case then trim to length. If I had the correct die I would not need your useless help Google.

It appears that I will be able to avoid having to buy any 38-70 dies. A sizing die alone is $130 if it is even available from C&H. A 3 die set is $265. The Buffalo Arms brass is a perfect fit. I am able to only use bullets of about .377 or less due to a tight chamber. My .380 bullets that I use or my two 38-55s are too fat. A loaded round will not chamber.  I have a Hoch tapered bullet that works for fixed ammo when the case is expanded with a M die and I can slip fit them into a BP case when expanded with a custom expander plug. For those cases that I over expanded, running them into a 32-40 sizing die about 1/2” brings them back to specs. 
Next week I will be shooting BP and fixed with the Hoch bullet.

I think the .380 Saeco might be too fat for the bore. I haven’t tried my 248 gr bullets yet. If the Hoch shoots well I will not worry about other bullets.