I've came across these and confirmed they'll work in Magnum of hydraulic roller cam LA blocks. I am planning on trying a set of the fast bleed downs in a 360 LA block.3.9/5.2/5.9 ENGINE - Lifters - HiPoTek
Those are made by Johnson hylift. I bought a set direct from them, but got the Direct Shot upgrade. I'm not sure how inventory is now, but it was getting low when I ordered months ago. The nice thing about getting them direct is you save a little money in the process.