Got bit by a little lever bug last year and picked up one or two that you dont see everyday.
What would be a good cast pill to use in the 375?

Can't help you with the bullet question, but I also got bit and picked up a M94 in 356. I have been wanting one since the 80s. I love it! I have been contemplating finding a nice cast bullet and load for it.

OGS

Try the Hornady 220gr Flat Point.

I have shot a few deer with them with reduced loads in a 375 H&H.

I have only recovered one bullet shot into a doe facing me at 175yards.

The bullet was recovered in the rear ham, perfectly expanded.

For cast bullets check out Mt Baldy, custom bullets i have three boxes in .358" a 158gr RNFP Lyman, a 240gr WLNGC, and a 280gr WLNGC. Also check out www.hawkbullets.com as they make hard to get calibers and i belive they make .375gr flat nose, jacketed bullets.