I can tell you that A12GX Heads use the same valve stem seals as the later E15 Pulsar front wheel drive engines,Haven't tried them on a normal 1200 though.
These are used instead of the umbrella seals because of the space limitations with double valve springs.
With the single valve spring setup of a standard engine umbrella seals work OK,if it isn't broken don't fix it.
If the valve guides are worn you can either replace the guides which then need reaming to size or you can have them inserted with "K"line bronze inserts.
These are a bronze insert with an internal spiral to retain lubrication,they are actually swaged into place and are very reliable,just make sure the right people fit them and they will last longer than stock guides.
Having worked as both mechanic and a machinist in a race engine shop these are the go for most reconditioning,I would use new guides for any serious race engine just as a matter of principle though.