The M-19 was made on a M-24 Chafee tank chasis. The gun tub was to the rear of the vehicle and the engine in the middle.
The M-42 was made on a M-41 Walker Bulldog tank chasis. The gun tub was moved to the center to make the guns more stable.
The M-42: (pic courtesy of board member Rylau.)

Please note that if either vehicle was made, either the M-24 Chaffe could be made in 1/18 along with the M-19, using the same chasis. If the M-42 was made. the already produced M-41 could be dusted off and used for the M-42 chasis. Maybe even a new paint job on the M-41, a really great 1/18 model.
How about it 21C, or some other "up and comming" 1/18 manufacturer?
TTT