Looking for Suggestions
I have the Green Viton O-rings from the AA-performance Gasket kit
And I also have the Viton Seal Kit (non-Green) from 914 Rubber
Which set should I use? Plan is to use Sil-Glyde Brake lube for Assembling
Would go with the Dow 55 but don’t want to wait another 2 weeks for shipping.
trying not to misstep but also want/ need to just move forward

My personal preference is to use whichever o-ring fits snug.
I remember having to buy two sets to get inner and outer to fit properly.

The inner is 21.3mm (black) the outer is 25.1 (Green) from the PET catalog

Agree. Earlier engines used small and large o-rings on the tubes. The smaller size was on the end of the tube in the cylinder head, and the larger size was used on the end of the tube that fits into the engine case.

Later 2 liter engines used the same size o-rings on each end of the tube, and they were the larger sized ones.

At least in my experience that's how it worked on early 1.7 engines and later 2.0 engines.

works this way from memory (did them about 4 years ago, think i have this right).

all the engines have the same black o ring at block end. 21mm

all the early 1.7s (pre EA/EB) use the red ones at the head end. 23mm

all the later 1.7s, (EA/EB), the 1.8 and the 2.0 use the green at the head end. 25mm

i'm doing those sizes off my memory.
the actual sizes should be in the PET maybe.
but basically thats how it works. red for early, green for later.
black on all at the block. pretty sure that is right, but you never know with the mysteries of the 914.

ps

i have a couple of old seal kits that i have had for 30 years.
one of those was what i used 4 years ago.
it was a universal kit had all the different o rings in it.
red, green and black.
must have been the way they were sold back last century?
was how i figured out which o-ring to put on where.

i'm guessing the kits are no longer around so you got to know the sizes.
it must be listed in PET?