Or use bulk straight hose in all positions but the top and bottom main radiator hoses. I do that on both my cars.
You MUST use at least a thermostat outer plate to put gasket in there, the gasket will not stay in place without the stat outer ring to keep it in place. You also need the thickness of the stat plate to fill the gasket out to proper thickness or eventual leak from not enough preload or squeeze on the gasket. I have pulled so-called bad stat housings back from the dead simply by adding a washer to the thickness of stat/gasket to make it thicker, the stock stat cover warps in at the bolt corners to release pressure in 3 spots and leaks then. The added washer makes the pinch point thicker and then it seals where it was leaking before. One of mine now running for years like that.
The stat must have its' small edge hole facing straight up to properly bleed. It must also have the proper size and spaced length disc on the backside or the heater will NEVER get hot. The disc moves back to shut off the port, that then forces the core to heat up. I have seen crap stats in the past that were not spaced right on the disc and they would not heat up, the disc would not contact the hole to seal. When that hole is not sealed the heater loop is bypassed.
If stat in right system's bled by the time motor is hot, I NEVER bleed them longterm.
The smaller round gasket seals the housing to the head itself.
I still use old school green coolant, it lasts longer than they would have you believe.