Just thought I'd share my removable nose cowling mount for my Kit 302 Cessna 170. So far it seems to be working well (not flight tested yet but survived a quick dart into a pile of bed pillows.)
Method, in case anyone finds this useful for theirs:
1. Small Neodymium magnets glued to three of four balsa blocks (found no need to use four - the bottom block is bare.) Found these magnets at Michael's (USA) and also Home Depot. (Note: If the diameter of your magnets are wider than the blocks, you need to offset the placement of each magnet so the block can rest fully flat on the firewall.)
2. Glue Balsa blocks with magnets along four edges of the firewall. This is where some measurement comes into play: The blocks must be glued onto the firewall far enough from the edge that they accommodate the width of block + magnet + washer. You can use a ruler to mark off the distance; I just eyeballed it with the loose washer stuck onto the magnet, marked the distance with a pencil and it seemed to work fine.
3. Glue blocks in place.
4. Place nose cowling over blocks, then, seeing through the cowling in bright light, circle the outline of the magnets with a pencil on the outside of the cowling. This will be a marker for exact placement of the washers.
5. Glue washers (I got mine at Home Depot) into inside of cowling using your pencil-circles as a guide. Done!
I could have likely gotten away with only two magnets - port and starboard but we'll see how this survives flight...