I agree with the others here, can't see the lifters being the problem.
If you do just want to change the lifters though, cheapest way is to get 2 rocker cover gaskets, 2 inlet manifold gaskets, the inlet manifold end seal gaskets and a new set of lifters (you used to be able to get exchange at some places).
Remove the inlet manifold complete with carb - saves an extra gasket if your a cheapskate like me :)
Take rocker covers off, loosen rockers and swing em to one side, pull pushrod then pull lifter out with long nose pliars - can be a bastard to get them out, coat new lifter in oil and slot it in, replace pushrod, align rocker and tighten its bolt down to spec
Clean all gasket mating surfaces, place inlet/end seal gaskets in appropriate place and put inlet manifold back on, tighten to spec in the correct order - basically inner bolts, across to other side the work you way out alternating between back/front bolts then drop the rocker covers back on with the new gaskets.
should be about a 2 hour job without beer