I'm sold out right now. But, I am doing some R&D on a new one that uses a JK shaft. The 1310cv flange is fairly common but, the problem is the quality of the 1310 parts you use. I had issues with several Tatton shafts only to find out they were assembled incorrectly with mismatched no-name (Chinese) parts. This discovery led me down the path to genuine Spicer parts. Once I started using quality Spicer parts, I can honestly say the shaft is much smoother than before.
Unfortunately there are a couple problems with the Spicer parts too...
First, the Spicer 1310cv must be field-built from individual Spicer pieces. Most cardan CV's can be bought totally assembled, and all you do is weld them to the tube and you're golden. But for some reason Spicer does not offer a pre-assembled cardan CV in the 1310 version needed. The cost of the individual parts is much higher than the cost of a pre-assembled unit.
Second, since the cardan must be field-built by the driveline guy...his labor is much more than it would be if it came pre-assembled.
All of this means the shaft price is quite high (over $450), plus the cost of the adapter. Quite frankly...a driveshaft like this should not cost more than $300. So to reduce cost & complexity, I am working on an adapter to use a JK shaft. That way you can buy whatever shaft you want...USA made, Chinese, or whatever and you will have more options than simply "use Spicer stuff or don't do it".