C9 heads solid flat tappet cam rocker loose when tightened . Need advice

Need help guys on a budget build till I can afford something better. I bought a 66 F100 with custom tube bagged chassie. It came with a disassembled .060 460 (473) D1ve block and C9VE-a heads. The engine was a rebuild but never ran. Previous owner disassembled the engine to  build a stroker that didn't happen. I decided to reassemble the engine to save it from rusting as it was doing and I need it for mock up. The engine is completely stock  minus a tunnel ran with dual 600 holleys and a Crower solid flat tappet cam and headers . The cam was provided with the engine so I decided to use it and this is where I'm needing help. Its grind number 317F     , 294 int and 305 ex duration.  .592 lift on int and .612 on exhaust at 108 centerline. P/N 22360. Seems like a pretty healthy cam for stock springs but I'm not racing , its cruise only but I'm starting to think they wont hold up. What I done so far was assemble the long block , install cam and lifters . Heads have screw in 3/8 studs . I have the stock cast iron style rockers and a set of comp roller Magnums that were provided but they are 7/16. Four pushrods are already bent as provided so I need a new set no matter what direction I go. Pushrods are 8.550  long. I understand the stock rocker stud , rocker arm combo is non adjustable however I put it on to see what happens and it bottomed out but rocker still flops around. I'm pretty sure I need to change the studs and pushrods but can I get some insight . Any help to get me going in the right direction. So far I spent 165 dollars in the build since I was provided with all bearings , a gasket kit , pistons and machine work done. Thanks in advanced.
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I decided to go to hydraulic flat tappet cam and sell the solid cam. any recommendations on a hydraulic cam while maintaining the stock heads and springs. I'm just building a stock motor for now till I get the restoration done. If I do decide to go bigger I can always put my 501 in the truck and build that 572 I been wanting for the Mustang.

thanks sir

Ok guys I went to a hydraulic flat tappet can and installed only two 7/16 x 7/16 rocker studs by ARP. P/N 100-7121 . Now I can use my new set of Comp roller rockers that came with the engine deal. New problem is to run guideplates because the rockers are going to fall off the valve . Question is why do you have to do any machining to the head to install guideplates? Is there a guideplate that does not require machine work.

Putting guide plates on your heads pushes the studs up, potentially creating problems with the rockers, etc.  But with "street-friendly" cam profiles as I've run, you may get lucky and be able to run plates without machining.  I've done it with D0VE-Cs and no more than .540 lift.  But then again proper rocker geometry wasn't in my considerations back then either... necessary for a street motor???  You decide