I have seen that there are two types of tube seals, Do you think i should go for rubber or silicon? Also there are to sizes, small and large, which one is for the 500cc engine?

The thin are for standard 500 with the concertina tubes. I have had no leaks with standard rubber but used silicon seals for the crankshaft; these are better.

Personally, I would go for the silicon seals. If you are fitting new push-rod tubes, you should be able to use the thinner seals as the tubes will not have been compressed shorter. If you are re-using your original tubes, I would be tempted to use the thicker seals as your push-rod tubes, having been used, and therefore compressed, will not have extended back to their 'as new' length.

vdlaan says i should order the thin/small ones, thick seals look also smaller in diameter so i wonder if they are for older type like N or D
And i will use the old tubes

Have you considered the adjustable tubes the VW tuners use. I have them fitted - and have three spare.......a recognized upgrade....

I am aware of those but not for this engine, this is a temporary head only recondition until i find a 650 engine. i don't want to spend money on this one.
i will consider all this add on parts when i will overhaul/upgrade my 650.
Thank you for mention it anyway.

Another option (when you do your 650 engine) is the spring-loaded push-rod tubes---and the beauty of them is that you can just compress them enough that you can fit them AFTER you have fitted the cylinder head--no more fafing around trying to get all the tubes aligned (and the seals sitting properly) as you try to drop the head back on.
Andrew---did you have to modify the VW tubes prior to fitting? I found them slightly too long for the 3-port head, and the Panda30 head has to have the push-rod tube holes in the head opened up slightly to allow the VW tube to pass through.

Im unaware of modifying these VW tubes- they were installed by my engine builder - sorry

Well i ordered both types silicon ones and see what will fit better.
Thank you for your advice guys

Thomas