Try the valve seals first. It can definitely be done with the head on. Use the rope trick or a compressed air to keep the valves closed. I replaced mine and it solved the smoking pipe issue. Do a search on here and there are threads about how to do it.

 

Yes, the rope trick works, but you can get a spark plug hole hose for just a few bucks. Run the piston to the top so that if the air seal is broken you don't loose the valve altogether.

Using the hose and with the rocker shaft off, you can knock this chore out in very short order. Don't forget to give the valves a wiggle while the spring is off.

 

We changed valve springs on my son's 350 Chevy, it was a quick easy job using compressed air and the right spring compressor.

 

i have the tool (came with compression tester). basically adapter between compressor hose and spark plug hole. I'm just scared a valve will drop. But if you say that works i might give it a try next time I have to take the springs out somewhere. if the piston is at TDC, the valve can't drop far anyway???? i'm thinking it should be possible to recover without even taking the heads off (in worst case scanario)

 

If you move the piston to the top of the cylinder you are working on, you won't lose the valve even if it drops, it won't drop so far that you can't pick it up and reestablish the air seal.

In fact you have to get pretty rough to move the valve enough to lose the air seal and have the valve drop. I've never dropped one, but it's plenty easy to just leave a ratchet hanging on the harmonic balancer and turn the engine before working on each cylinder so I've never taken the chance.

With the piston at the top it won't drop so far that you can't just pick it back up.