A floating clunk (not a good idea for other reasons) wouldn't make any difference in pressure at all. It's the head pressure created by the level of fuel above the carb that's important and it doesn't matter how the head pressure is created. In other words, your floating clunk will produce the same head pressure at the carb as one at the bottom of the tank with a given fuel level. Fluid Dynamics 101.

If you are using an engine with a Walbro or similar carb I think you can probably forget about it. They have an internal fuel pump and pressure regulation system that eliminates head pressure changes from the tank level (and attitude).

If your engine is not using the Walbro-type carb then you need to get and learn to use an after-market pressure regulation system such as the Cline or possibly the Perry/Varsane. An 80-oz. tank with a non-pressure regulated fuel system is most likely gonna be trouble.