I am reasonably sure the .40/65 Winchester is made on the same case as the .45/70, if you could live with a bullet 0.10 smaller in diameter. .38/56 WCF too. Many of these cases were developed for Ballard, Stevens or other "match rifle" makers and borrowed by Winchester for their lever actions. That .45/60 WCF was pretty lame but then Browning came up with the 1886 and it would handle the .45/70 for whick cheap surplus ammo was available. Lower pressures. .30/30 and under. .406 bullet.
Most assuredly, the .450 Marlin will be necked down if it hasn't already. The Rifleman loudly proclaimed its purpose was a much stronger case than the .45/70 to give equal or better preformance with the better feeding reliability with a belt than a rimmed cartridge. You might care to examine Mike Bellm's house cartridge line on the .444 Rem case (bellmtcs.com). Same thinking. Great for single shots. His specialty is T/C products, or had you guessed. Or did you want a repeater? LUCK.
