Looking for replacement seat belts

I'm looking for seat belts out of a modern car that have similar dimensions to use in my Datsun.  These boxes tuck into the car and measure 4" deep x 4" tall, and 4" wide.  The mounting tab is actually 2 additional inches on the "tall" dimension, and it bends inward about 0.5".  I can replace the receiving end too.  I've been scrolling through ebay trying to figure it out... any tips?  THANK YOU

In the car:

And out of the car:

They look like a nb miata would work. 

Also possibly rear seat belts from an extended cab gmt400 truck 

Well that was quick.  Thanks.  It really is the answer

Another option is aftermarket belts:

https://www.seatbeltsplus.com/category/3-Point-Retractable-Seat-Belts.html

I used Seatbeltsplus for belts forone of my Triumph Stag project.  I was pleased with them.

Try early Miata ones - they look to be similar size (I have Miata belts that fit with minor modification in my e30, for that matter)

Another option is to check British car parts places like Moss or Victoria British. A lot of British cars (like MGB, Spitfire) are close to the same size and had 3-point belts.

Moss is closed for the duration. ' Moss announced today that out of caution and concern for the health of its employees and customers related to the COVID-19 pandemic, the company will temporarily close its operations nationwide effective Wednesday, April 1 at 4:30 p.m.'

Victoria British has 'As a precautionary measure, we are temporarily closing all services for Victoria British Ltd. until further notice.'  

The Roadster Factory is still shipping.

You could try Matthews Foreign Car Parts in Birmingham, AL.  I've dealt with Richard a lot when I was redoing my TR7.  His son Dave Matthews is selling a lot of on Book of Faces.  They had a 6 story building full of parts, Brit car, SAAB and Yugos.

Aftermarket... My impression was that most of them mount with the mechanism "out" but I'd prefer them in the recess of the wall.  I do see that company offers some for a miata that do go inside.  I will have to call them.  

Does anyone know if the buckle end is a standard design?  I definitely need a longer receiver.  

I have bought replacement webbing in the past. Can you just restore what you already have.

No.  These don't lock on a sudden jerk only on deceleration or facing downhill. It must have some kind of pendulum in it.  I really want ones that lock on a quick pull if possible

You're right. There is a small mechanism that can sense acceleration/deceleration and any movement of the vehicle out of the horizontal position. It's either a pendulum or a small steel ball sitting in a cup. If you use a seatbelt retractor from a different vehicle you have to find one that has the same installation angle as your car. In your first picture you can see that the B-pillar is slightly tilted to the back of the vehicle. If you would use a retractor that was originally mounted vertically, the mechanism might lock all the time and you would not be able to pull out the webbing.  

mikeatrpi said:

No.  These don't lock on a sudden jerk only on deceleration or facing downhill. It must have some kind of pendulum in it.  I really want ones that lock on a quick pull if possible

If that's what you want, you may need to find older belts.  Most manufacturers changed from the friction/impact style to impact only, because people hated them.  

And, they have to be a perfect fit, as stated above. 

Interesting.  I guess I'm not sure what the right term is.  On both my 2014 Forester and 2006 BMW, a quick jerk of the front belts locks them up.  If you pull them all the way out, they lock and stay locked as you feed webbing back in (for car seats, I assume).  Gradual pulls of the belt does not lock them up.

On my Datsun, you need to be facing downhill or be decelerating.  As soon as neither is true, the belts move freely again.