Looking at pictures of both New Idea and Oliver sub-frames, they look similar but I don't know if they are interchangeable or not. I have also heard stories of people mounting a New Idea sheller on an Oliver picker (or maybe it was the other way around) so they may be interchangeable. If you were closer to me, you could come and measure the frame on my New Idea to check. I used to have extra subframes around here from New Idea pickers that I had parted out but I think they are all gone now.
Do you know anyone that has a oliver 74 H who might be willing to share some photos of the mounting frame. I have an operators manual but it really does not show the frame - don't know why. I may be able to make one if I had some pictures and measurements.