Lifter (Tappet) conversion '87 2.3-19v

[spanish cossie]

Hi all, I have a 1987 2.3-16v Cossie and my compression readings are 5.5 across the four instead of 9-ish which kinda explains the crap starting and lack of power under 4,000rpm, I don't use any oil or leave a trail of smoke so I guess rings and valve seals are OK it must be tight valve clearences as they are manual shim type. If I am going to lift the cams out, as one must, to change the shims I was wondering if one could fit the post 1988 hydraulic lifters instead as these are a 'fit and forget' item or does it mean a head swap?
any one know?
Peter