doubt wether u can do em without takin the head off to be honest but maybe someone can say why they think u can. take ur head off and take cams an lifters out and ul need valve spring compressor to take valves out.ford list special tool to remove cos ther quite deep. If ur very confident u can split the old ones off by using a long screwdriver with the end sharpened and tapping with hammer but be careful not to damage the spring cup seats under the guides. if u then find a socket size that the new guide sits nicely in u can tap them home with extension on this an little bit wd40 on new guide. ul hear an feel wen it seats.replace everything as it came out, and if valves are black clean with rotary wire brush.use cometic cam cover gasket as ther reusable, ford ones are rubbish.Clean head and block faces with fine wet and dry and use standard 4x4 h/gasket 10 quid from woodfords at moment, and new head blots.replace any other gaskets u disturb, inlet manifold etc.jobs a perch.