You will need to remove the rockers before you install the new cam and towers, and then you will need to compress the valves to reinstall them (or new ones). You might as well buy a compressor now and take out what rockers are accessible.
You will still have some pressure on the bolts when you remove the cam and towers, but I doubt that you will strip anything. You really don't have much choice.
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe