First of all check the 16 ga chamber length. It will almost assuredly be 65mm.

For the 6.5x70R try 25gr of IMR 3031 and a 120 gr Speer Spitzer. It shoots about like a 25-35, or a bit under. It is not a good caliber for anything bigger than roe deer. It is an uncommon caliber. Do you have dies? A Berdan priming tool will porbably be necessary, also. I have no idea where to get brass.