You do have to notch the block in most cases with the i beam design of rod like the Scat or Maxspeeding, however you can get Pauter rods which are very good quality and light which you pay for and they have clearance being a x design.
Been waiting for one of these to come up for ages, there getting really rare with fogs as well. Wrong time unfortunately, good luck with the sale
Whereabouts are you Adam?
You should be able to give them a little squeeze one way and then the other with the pliers and then wiggle them out. You'll get it down after a few. Or they do actually manufacture special pliers specifically for the job. Seat the valves either way, I lubricated the guide and seal when doing so.
They differ in design and the material content which can effect weight, expansion and strength. However for most application the capabilities of any will be fine, it's only when really pushing the envelope careful consideration needs to be given.