one TOKE over the line... 
We used a brand called "TOKE" that made "umbrella" seals for the chevy motors,(and most all others too) at the machine shop in the parts store I worked at..they are made right here in my home state (at least they were--its been 10+ years since I worked there--not sure if they are still around,but they probably are--been around for many years..)..
I think 302 ford ones will work,and are similar,but I'm not 100% sure..I'd ask your local auto machine shop about the TOKE brand"Umbrella" seals.(they call them umbrellas because they look like one--stock GM ones are just "O" rings!).--they dont cost much,and are fairly easy to install--IF the valves dont fall down into the cylinder with the springs off.
Doing them with the motor IN the truck sucks--its best to do them when the heads are off for a valve job,since most engines that smoke due to bad valve stem seals are likely to need a valve guide or two replaced or knurled,and possibly a valve job,by the time that many miles have passed..not always though...
..You'll need an air compressor,valve spring compressor,a magnet to pull the "keepers" off the valve stem(and be very careful not to lose them IN the motor!)...and a strong back and lots of patience to do them with the engine in the truck..it'll take the better part of a day,if all goes well..putting the keepers back in without losing them is the worst part--next to bending over all day,and cringing when you start it up the first time,praying all the keepers went in right,and no valves fall in the cylinder!
