So how far do you go...? 240D Top end

[Fisherman]

Okay,
Smoking problem on the ole 240 so I took her down to replace the IP diaphragm and found that the reason it wasn't holding vacuum is the screws on the back of the IP were loose, duh. When in doubt check the obvious first...
If anyone sles has a 616 motor then heaven help you if you want to pull that bottom nut off the IP. That alone took me 2 hours and it didn't come off until a friend with long fingers helped out...

Anyway, I have a leaking head gasket above the block heater so figured as long as I have the IP off and so much room on that side of the motor why not do the head gasket.
So, here I go taking the head off the car.

My question is, how far should I go into the head before I start hitting the laws of diminishing returns? I figured I'll do the head gasket and timing chain. Stretch by aligning marks is at 7 degrees. But how much further?

Should I just inspect the valve stem seals or just replace them since I'm able to get to them easily out of the car?
Have the head checked by a pro or just eyeball the valves and let it go if they look fine?

I hate to put too much into this car as it only cost me 425 and runs pretty darn good, but the body and paint are not exactly cherry so I'd hate to put 425 into the car and then be able to sell it for 800.00...

Any thoughts?

[MS Fowler]

If I were pulling the head, there is no way I'd put it back on before I had the machine shop go over the head. I would expect a complete valve job and new seals, and guides if it needs them.

By the way, I don't think that "lapping" valves is accepted practice anymore--I believe a proper three angle valve job and a fresh face on the valves is the only acceptable way to go.