It Runs..sorta..

[Walt_M.]

My granddaughter would say, 'if you can't say something positive, zip it', however. Are you planning to mount a camera to view this sight glass?

[The Prophet of Doom]

My granddaughter would say, 'if you can't say something positive, zip it', however. Are you planning to mount a camera to view this sight glass?

Why would you need to?
The sight glass will tell you at rest if the levels are correct.  Enough to see you through your next ride

And what adhesive would you use to hold the new lens in place?  It would need to withstand continuous contact with fuel.

Any of the fuel tank epoxy putties would do just fine I'm sure. 
I'd prefer something screw in like this
Holley 26-112 Holley Sight Plugs | Summit Racing


Price is OK, but shipping cost to NZ is 10 times what it actually costs

[pinholenz]

And it would need to have a lip to sit on so simply drilling a hole would not work.  Perhaps drill a hole and then ream out the sides to create a 1mm lip?
POD, a range of watch glass sizes are available in NZ from the "Time Centre" watchmakers supplies in Auckland. Alternatively, as cheap as noodles from Aliexpress from China.

[injuhneer]

I have used JB Weld Tank Weld epoxy on all sorts of fuel system repairs.

I'd probably use it to seal the crystal in place.