Measuring piston to valve clearance on my b18c questions

Hello just a couple of questions.

As the head is taken on and off to install and remove the playdoh, if I’m using a new head gasket is this head gasket now not usable for the final assembly?

And once the playdoh is installed for checking for piston to valve clearance and the cams have been installed using the factory Honda marks. When I then want to find true TDC following the method as described, does this mean the piston stop method can’t be used as the playdoh will get in the way?

Or should true DTC be found with the cylinder head removed using the deck method?

Or have I got this completely wrong.

Since the engine hasn't been run then you're fine to reuse the gasket and you don't need a new one for the final assembly. While I don't recommend it myself, many engine builders will happily reuse an MLS gasket even after an engine has run.

If you want to check piston to valve clearance then you actually need to degree the cams before putting the playdoh on the piston otherwise you're going to get misleading results. You only want to turn the engine through a single engine cycle with the playdoh in order to perform this check.