I don't think it should have any effect on the handguard, the bit which holds it on at the front is the metal 'cap', which is attached to the front sight via the gas tube (as far as I can tell!).
In theory by replacing the front sight with another gas block the plate should sit in the same place without a problem...maybe.
Edit: had a look at the exploded view on http://www.greekairsoft.gr/manuals/manual.asp?Manufacturer=KING+ARMS&Filename=King+Arms+Magpul+PTS+MOE+Manual.pdf does look to be that way.
My main problem with that ebay gas block is how it tightens on to the barrel, kind of looks like it's just a grub screw which bites into the barrel. If so, nuts to that.