One thing about those smaller radials... I had one of the 3-cyl Saitos but I sold it. Compared to the engine weight those engines do not pack punch, they are LAZY!!

You need to severely over-engine your aircraft to get even a decent performance. You want a radial for scale looks and sound. 3-cyls do not have that much of the appearance because they lack cylinders but they sound very good. But sound only does not take the bird to the sky.

You are now looking for a radial in around 2 cu in? I for one would not even think of anything under 3 cu in if it was a radial. Problem in that category often is that the single row radials have too big outer diameter for most applications with the outside dia being around 220-250mm range. Smaller Saitos are around 185mm to less with the 90R3 that is the smallest but those tiny radials are too heavy for almost any bird. That beautiful Hughes will be a dog on the verge of stall all the time with that 200R3.
In order to increase fill volume you would need a 7-cyl radial. Technopower makes (or used to make) those but the Technos have a reputation for even less power than the Saitos. Other solution would be a 10 or 14 cyl twin row radial to keep the diameter down but I have never seen a commercial twin-row in the market. One-offs are there but rarely for sale.

80" WS can carry a lot of weight so a bigger radial is not bad at all. You dont need the Hughes for 3D, you need it to be able to fly fast (which is scale flying for that airplane) and sound good. And land decently. I am planning to buy the same kit and if I decide to put a glow radial in then 325R5 is the minimum I can think of.

Another idea for you... have you considered a rotary engine? I have another 82" WS warbird-vintage speedracer sort of that I modified from an ARF kit with drastic changes and I will equip that airplane most likely with a Sachs Dolmar KMS4 rotary engine. 57cc, 8hp@8000rpms. Overpowering? YESSSSS !! I love that. If it was a 3D-plane then that would be different but flying fast with no crazy sudden maneuvers then the fuselage and wings will be ok.