I have a 90 EX Fujinon that is excellent even though I generally use a 80mm Componon mainly for the 'ease of use' features, so agree with OnF, keep an eye out for a fujinon
Most likely 39mm as others have said. I've seen some older 80mm in 32 or 25mm, but never anything as long as a 90. FYI, the lensboards for the Beseler 23 and 45 are the same.
I don't have the Fujinon brochure for the ES, but the EX brochure shows 50,75 and 90mm lenses in 39mm (26"pitch; Leica) mount while the 135mm is shown in 53mm (0.75mm pitch) mount.