Ticking sounds engine

Without hearing the noise I can only guess. Probably a hydraulic lifter. Many 50s, 60s and 70s engines had this problem. Varnish builds up in the lifter body. If it's just a SLIGHT tick, I wouldn't worry about it. You could try a different brand of oil and some engine cleaner.

As an aside, I personally own a 91 GMC pick-up with a 4.3. It had a clicking lifter on start up and 10 min after. I always used Castrol oil, supposedly one of the best. Switched to Penzoil, it was on sale. No more click!

If you want to try and un-stick it, try this. Be forewarned, it WILL make a mess! Try and locate which side of the engine the noise is coming from. Remove the valve cover. Inspect for bent pushrods and rocker arm stud pulling out of the head. If you find either of these problems, disassemble the whole valve train and inspect/replace worn parts. Back then, Pontiacs and SBCs were notorious for studs pulling out of the head if you ran them hard.

Start engine. Oil will spray/mist everywhere. You were warned. LOL
Watch the rocker arms as it idles. If one does not move as far as the others, and the click is more of a bang, you have a collapsed lifter. A worn cam lobe will be much more quiet than a collapsed lifter, but you will see decreased movement of the rocker arm. Replacement is the only option on both.

Take a RUBBER (not metal ) or plastic dead-blow hammer and rap the rocker arm(s) several times where the pushrod mates with it. Over the years I have used this method with approx 60% success.