Hi Carlo,
I am able to adjust the valves on my 48 Plymouth with the Fentons in place. Remove the right front wheel and the inner fender panel. You will then be able to work straight at the side covers and adjusters. I warm mine up a bit and let the manifolds cool off a little before I get in there. I then adjust the valves by turning the engine over by hand (remove the spark plugs). You can adjust valves with the engine running by sticking the feeler gauge in between the valve and the adjuster. It will go and can be moved in and out as the valve moves and clearance is obtained and taken up. Kind of jurkie, but you get used to it. Just wait until you try to get the wrenches on a moving tappet! It's just too hot that way for me, so I just leave an extra thousands or two for expansion.
Jim
