A “CB Performance 2L” was all the info the PO had.
A LOT of Beck Spyders got either a 1915cc or a 2165cc. It's probably the latter. If you ever pull the heads you'll be able to know for sure.
Unless you put it at BDC, remove the rockers, and fill the cylinder through the spark plug hole. That would give a pretty good ballpark, just multiply by 4.