Yes, Belcher makes the limbs for 3 rivers, including the longbow limbs.I purchased a set of dalaa carbon foam LB limbs and have put them to the test for the past couple months, here's my take.
Mine are 45# med limbs making a 60" bow with the 17" dalaa riser. My draw is 29" so I'm pulling #48. The limbs are smooth drawing with no noticeable stacking. The limbs are as fast as advertised. I shoot a 500gr arrow at 173fps. The negative is I find the limbs after the shot are harsh (hand shock), and somewhat noisy. Don't think the first I can solve but still working on the noise. These limbs were $459 the wood carbon limbs are $299. I think the wood carbon are less harsh and quieter than the carbon foam based on the recurve limbs (I own) from the same maker which are wood/carbon. They are also 5+ fps slower. Hope this helps. My limbs and riser are in the lost camo,which are nice but I actually prefer the natural gear camo but its currently not offered.
One more thing the LB limbs in both carbon/foam and wood/carbon are quieter than their recurve counterparts, and I have found no difference in the speed, recurve vs longbow limbs.