Leave the oil sender or remove its up too you.
Just make sure the oil is on the dip stick where it is supposed to be.
Never run less than 600ml of oil ( unless you racing where less means more power and less foamy oil )
I am not familiar with the current crop of GX series engines.
I suspected there was something like you said about piston pop up on the 160 looking at the new series of heads.
I suspect its the piston that is different and I suggest the ZH8 or Z4M as an alternative ( it will fit trust me )
In Thailand these pistons are about 10 USD at the dealer.
You are in he right place to find clones too, that is a very competitive area for engines and parts.
My suggestion is strip every blown engine you can find and look at it.
Most engines fail because of lack of oil.
but these are not always a right off.
If you put the crank shaft of one of those engines in bath of KOH ( caustic soda + water ) this solution will eat the aluminum off.
they you polish the crank with some 400 grit, them 600 grit in a cross cross pattern to make it shiny again ( very hard to make out of round if you count the number of strokes and move often )
You max clearance on the rod is .005.
you can cheat and sand .002 off a rod cap but more than this will cause trouble.
These are some of my dog motor tricks for making scrap run.
In conclusion Koen you want to find a head that has a small chamber and looks like this
You would be better to chose a piston that does not pop up above the deck as you have found in the new engine you opened up ( still a good engine but you must be careful about gaskets ).
You want to measure from the top of the piston to the flat part of the head squish area about .030 minimum space to make sure the piston will not contact the head.
more clearance is safer from a piston strike, but tighter makes for better performing engines