Floor issues converting 73 duster from automatic to 4 speed

I'm in the process of converting my 73 plymouth duster from an automatic on the column to a 4 speed on the floor. I purchased from Sherman parts the sheet metal  transmission hump for the floor shifter 195-40c. It fits well everywhere except at the rear of the piece next to the drivers seat. It has about a 2" gap around the end where it would attach to the floor. I looked at Year 1 and it appears to be the same part. My question is ... Was there a different floor between the automatics and 4 speeds that rises up higher under the drivers side front seat? Has anyone done this conversion and run into the same issue? If so how did you fill the gap?  Any insight from anyone would be helpful. Thanks..