Cassp
When I was gigging with a B3 I had a bass unit called a NOVA IV installed and had synth bass tones with sustain on both the lower manuel and pedals. Also had its own volume controlled 1/4" output.
You can get sustain on a Hammond with a String Bass unit from Trek II products in New Brunswick NJ, They make top quality add on and replacement parts for all model Hammonds. Until recently I did a lot of buying and selling of Hammonds and did business with them.
The last B3 I have is my personnel one. A MINT 1958 Cherrywood with matching leslie, String Bass, Fischer Reverb, new covers, etc. Interested?
I can make your dream come true

Bill in NJ