<font face="Verdana, Arial" size="2">Fast91SER askd:
...would i have to get it from a canadian one?</font>
I honestly don't know, as I've not attempted to relo the shoulder belt from the door to the B-pillar. But, here's my guess:
First, you'll need a bolt for the upper belt mount. Source Nissan for this one - my bet is it's a standard belt bolt like the rear belts use. Next, fab a spacer for use between the B-pillar and trim. Third, source an upper shoulder mount, like the rear shoulder belts use, to use on the B-pillar. There, the upper part of the shoulder belt is handled.
Now, for the bootom anchor, I don't know what the stock belt looks like in the door for US models, but I'll bet it's a simple fitting and bolt arrangement like the rear lap belts use. Given that there's a shoulder mount in the chassis for CDN market B13s, I'll bet there's also one for the bottom mount under the carpet or lower B-pillar trim (I haven't looked). It can likely be handled in a similar fashion.
Frankly, I think the idea of this setup is pretty nice and far safer than the door-mount setup that comes stock. The only potential drawback is rigging your belt setup like this will make rear seat access on a 2-door more of a pain.
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'91 Classic w/the usual stuff
"It is better to go into a corner slow and come out fast than to go
into a corner fast and come out dead" - Stirling Moss