Just my recent experience with seat spring cores.
Back in December I started looking for 2 seat spring cores, several vendors said they where NLA. Finally one highly reputable vendor many of us use in US said they had them, and I purchased them. The pics from the vendor looked exactly like the SLS pics in Hauser's link.
I contacted several vendors who know Pagoda interiors, not just the local upholstery shops, about redoing my seats. When I sent them the pics 2 vendors said the seat spring cores I got are for a Ponton and would not work, the third said there is a 50/50 chance they might work with some modifications. The vendor I got them from said to return them for full refund and they even paid for the shipping.
I am not saying the SLS are incorrect, but they maybe, I would just be very cautious. If someone does get them from SLS and they are correct, please let me know, I will be next line to get them if they are indeed correct.
Alex