Never used an estoril but biturbo's are pretty loud so i wouldn't be surprised.
strap wrench looks something like this
Put the strap around your magneto and use it to hold the crank into place while you remove the nut holding your clutch bell on.
Most people recommend this as it keeps you from pressing your piston up against anything and risking damaging it in any way. If you do end up buying a piston stop get the extra long one that treats sells. That's what I use and haven't broken anything yet while using it. You do have to be a little more careful though when you go this route.
Basically when you try to remove the nut holding on your clutch bell you'll end up just spinning the crankshaft and never be able to loosen the nut unless you use one of the methods I listed above.
Using a strap wrench is not only the safest method but you can probably get one locally without having to get it shipped to you.