hi guys, i have a 87 4wd, has about 210,000 miles on it. i think its the original engine but not sure. it runs great, doesnt smoke, doesnt over heat but it has this strange clicking noise from the engine at start up and low speeds, usually at fwy speeds the noise goes away. my oil pressure at idle is on the low end of the gauge. warmed up at fwy speeds it gets up to about half. is that normal?

ive been doing some research on the site and it seems like i might have some stuck lifters? how can i check them and is it possible to change them out without removing the head?

if there is a write up on this anywhere i would greatly appreciate the link. or if anyone has had the same issue, any advise would be great. thanks!