I made my own pick-up for my round-hole (home made) guitar in the school metalwork shop.
3 wound coils from old RAF headsets, were screwed into a mild steel bar which was under slung in the guitar's 'round hole'.
Some small round magnets were placed on the mild steel bar to increase the electro-magnetic signal - when they didn't fall off, that is.
A wirewound pot'meter for volume control with a nice big round brown bakelite knob, wired to a bakelite backed phono socket. Cream coloured pick-up cover was fashioned from a carved out yogurt pot and Airfix glue - very Fender-like.
Summer 1970. Shame the guitar's neck was too badly warped to play, though...