I believe that the rumble seat side brackets are available repo from I & I reproductions or THE FILLING STATION. The latch has to be moved to the top when the lid is spun around.
Also as one who is converting a 1935 std rumble seat roadster to NON rumble seat. You will also have to remove the bottom rain gutter completely so the lid can rotate to the open position. The side rain gutters will also have to be shortened , again so that the rumble seat can pivot to the open position .
NOTE....a 2" x 2" length of oak that goes from side to side has to be installed on the floor so that the lid can only rotate so far.........as a lid stop. Go too far and your going to put a crease in the lid.
Because your losing the bottom rain gutter and about a 1/3 of the side rain gutter your going to have to arrange the floor so that the water runs out the rear corners with holes in them as drains. Failure to get the water out will mean premature rust and rot out of the floor.
A rumble seat floor should be different than a regular non rumble floor. My 35 roadster has specific foot wells in that area ahead of the rear end. It drops down about 5-6". I had to remake mine as it looked like a swiss cheese once I got the bondo, fiberglass, tar and whatever else was covering it up.
Luckily we have enviro tech strippers here that chemically cleans the surface down to bare metal and removes everything not steel.
Re the roll down rear window. You will need the " complete" roll down mechanism from a 33-34 master to be able to update to a roll down. Been a couple of years since I have seen one offered up on here or ebay.
Also you will need a ***water trough*** to go under the rear window, it has a drain pipe on one end to get rid of the water running down rear window. The glass channel holder lynn steele rubber now makes the rubber for it, same as side windows. The window roller that keeps the glass in align in the middle, the little rubber barrel roller is also available from I & I repo
I have I believe a 1933 chev coupe master rumble seat floor section and also the rear floor section with the holes in corners. The guy I bought it off wasn't sure which year...3 or 5 window it all came out of. Its in perfect condition.
Also finding the correct rumble seat lid seat and back rest cushion springs may be difficult. Not sure if a 33 rumble seat lid has a metal inside liner or an all wood construction that's nailed thru the metal to the wood like the 34-35 std roadsters.
mike lynch