I would love to see some post mortem pics of the old engine, specifically the crankshaft, bearing caps and bearings. From the video I saw I heard the rods knocking but I’ve read the top end was also making noises? Usually if there is a loss of oil pressure bad enough to affect the top end, the oil warning light will illuminate.
If I had time and space I’d love to take the job on. Sounds like a crank regrind and a set of oversize bearings, maybe a set of rods if the bearings spun would fix it but without seeing inside and doing some measuring it’s pure speculation.