I installed a Dubro 16 oz fuel tank in the Venus II.

I had to remove about 1.mm on each side of the slot in the former in front for the tank to fit in sideways. With the tank chin mounted to the right, that lines up the tank stopper with the hole in the firewall.
A strip of foam padding on the chin. around the former and at the back of the tank as well a 1" thick piece of foam above the tank all fit just like the supplied tank.

This will make the 10 minute flight with ease.