11 on an 8

[Sum]

If the wheel has a 8/9 speed freehub, then you can use either a 8, 9 & 10 speed cassette or a MTB 11 speed cassette. The smallest 11 speed MTB cassette I can think of are the 11-34t CS-HG700-11 or CS-HG800-11 (105 & Ultegra) cassettes. Technically they part of the line-up for the 105 and Ultegra road series,

https://si.shimano.com/en/pdfs/ev/ULTEG ... _PARTS.pdf
https://si.shimano.com/en/pdfs/ev/SHIMA ... OP_v01.pdf

but I call them MTB cassettes as they come with the 1.85mm spacer that allows them to be used on either 11 speed MTB or road freehubs. The pitch between these sprockets is reported to be 11 speed MTB pitch (3.9mm) rather than road pitch (3.74mm), although they still seem to work with a road drivetrain.

If 11-34t is too wide a range then your choice is restricted to a 10 speed (or less) road cassette or modifying a 11 speed road cassette e.g. removing one of the sprockets. Although I'd only do the latter if I already had a 11 speed shifter and derailleur I wanted to use.

[Mick F]

No idea about Campag freehubs.

Campagnolo don't use a freehub like wot Shimano do.

The freewheel assembly is a separate item held on by a nut thingy (P).
The RH wheel bearing is in the body of the hub.