Obscure Movie Search

Ok. Really weird search here.

I'm searching for a really obscure movie that I once saw at a drive-in way back in '76.

Set back in the old west, a cowboy runs across an injured Japanese, who is trying to return a box or such to someone in Japan for a reward. The Japanese guy dies, and the cowboy takes up the quest for the reward, and takes a ship from San Francisco, and brings along his horse as well.

There was an excellent scene where the horse is unloaded to the docks in Japan, and is unsteady and stumbling about, trying to re-gain his balance on land after being at sea for so long a voyage.

Other memorable things I remember in the film was a cross-dressing Samurai, and an old blunderbuss gun the cowboy found, that blew up the end of the barrel when he first fired it, but then he tied the shortened remains of it to a small log and turned it into a shotgun, and started kicking ass.

An obscure movie to say the least, but it was actually very entertaining. Almost 'Evil Dead' quality stuff.

It's one of those things that always stays in the back of your memory, like a constant itch that you can't scratch.

Any help or ideas from someone?