So you have a 1949 Gibson L-50 Archtop.... "The pickup is a piezo bridge for an archtop but the preamp is for a flatop acoustic so the impedances don't match". Wouldn't the guitar tech say...You want me to do what to this guitar? I wouldn't have done it and thrown him out of the shop.
"I've been told this and it's been proven by research - He who fucks Nuns will later join the Church"
Gee! I recently restored a 1940's L-48...just cleaned the finish, polished the metals, and replaced a severely cracked bridge base with an era original, and set it up....what a guitar! If anything I would have installed a K & K Piezo with no electronics....easily removable with no alteration to the instrument.....oh well!