'67 Mustang 289 V8 Loose Rocker Arm Polylock Nuts Wtf?

Trying to tune and road test my '67 Mustang 289 V8, but for some reason, the POLYLOCKS KEEP COMING LOOSE, and not always on the same cylinder or bank -- sometimes left, other times, right. I'm confident the valve adjustment procedure and pre-load and zero lash have been done correctly (performed more than once so you tend to get good at these things. LOL!). Engine is a 289 +.030 has a fairly aggressive "street/strip" cam (290/228, .504 lift), Comp Cams Roller Tip "Rail Type" rockers AND using polylock nuts (some type from JEGS I bought years ago. YES, heads were machined for screw-in type studs, but no guideplates. Carb is EDB 1406, brand new out of box, and I've adjusted float level, etc.

I'm thinking of ordering a set of replacement STOCK TYPE rocker ball and nuts kits from Summit Racing. Am I just NOT cranking down the polylocks enough to keep damn rockers tight for more than a few starts? Just don't want to bend any pushrods or valves at this stage. Thanks for your input and shared experiences with this PITA issue.

Thanks for the reply @tos. I rebuilt the top end on this engine 15 years ago with an Erson Street/Strip Hydraulic Kit (cam, lifters, dual springs, double-roller timing chain, pushrods, screw-in studs) from Super Shops in Spokane, WA. The polylocks I installed (see photo below) are meant to fit early Ford SB 289-302 and even SB Chevys with a 3/8 screw-in stud. Actually, these parts have very little running time and driving miles ever since the T.E. rebuild. Bottom end was rebuilt .030 over just before I bought the car back in '91.

This car has been an on-off-on project over the years. I can usually get the valves adjusted, and with some carb tweaking, the car runs really smooth, even with a "fairly radical" streetable cam profile. I'm going to order some stock-type rocker arm nuts from Summit and relash the valves again.