I am not an engine builder but I built an LA 360 years ago and currently building a Magnum roller 360. Dunno your amount of expertise but the quality of hydraulic flat tappet lifters has been a major issue over the past few years. I would consider disassembling your current lifters and inspect them. Also pay close attention to the cam to lifter contact surface. The lifters must be slightly convex to spin properly in the bores. Make sure you soak the lifters in oil overnight and use plenty of engine assembly lube on the cam, lifters, pushrods and rockers. Prime the engine and check for oil flow to valvetrain. Use a good quality break in oil with high zinc/zddp. Car must start immediately. Avoid excessive cranking.