Modular vs. Pushrod engines

I've read a little bit on modular engines. But I still do not understand why or how they can only have 4 or 2 valves. How do they work? What is different about a modular engine? Are they all overhead cams like imports? My brother has a 4.6 Mustang GT with such and engine. When we work on it is there anything special that needs to be done??

sell the stang and buy a camaro. i like my camshaft below the pistons

yeah, this is a question for the stang forums, i dont know technical specs on the modular engine. just chevy iron and aluminum