To add to Bigmoe's comment I changed out valve springs both ways, air and, in my case, an old spark plug lead - you will need to remove the valve springs to replace the seals.
It is really rather simple - don't be afraid to give it a go - and if it doesn't go according to plan take the head off and use the opportunity to do the valve job.
Looks like a really nice truck.
Enjoy!
P.
