Hi Craig
It all depends how handy you are with a bag of spanners.
I changed the camshaft in my 3.9 when i bought it, it was the reason it was cheap, i fitted a performance one as a replacement, made a differance and now i have a free flow air filter, 4 branch stainless downpipes and twin hand made exhaust with no cats, that lot made a world of differance.
I think it is an easy job, drain coolant, engine oil, remove rad, undo crank pulley before removing plugs, intake manifold, rocker covers and rockers, push rods and front cover, not much more, the worst part i found was leaning over the wings to get at everything.
As for the crank bolt, i used a good socket, breaker bar and a big hammer or:violent:
:hysterically_laughi
Ian