What size cowl ?
I did a cowl for a Bellanca Airbus (circa 1930's) that was attached with a combination of socket head screws and magnets. I could get at 2 screws with a looong homemade allen wrench and the other attaching points I imbedded magnets into "L" brackets on the inside of the cowl and steel plates (strips) imbedded into the firewall. The plane is powered by an Evolution 46 NT.
I got a hold of some 1/4" square magnets. Each magnet has a 6lb - 8lb holding weight. I used 3 magnets and 2 screws for the cowl plus steel 1/8" bolts embedded in the speed ring and magnets imbedded in the front of the cowl (with 2 3/32" dowel alignment pins).
I fly off a grass field, so some of the takeoff runs have been bumpy and "some" of my landings have been "on the hard side"
Nothing shifted or came loose.