I would size the smaller turbo closer to th ehx40 size, and go big on the bigger turbo. I too am looking at a C or ISLin my project truck.. truck isa based on a '99 sd F550, looking at 1950 willys jeep pickup cab on it , rear is dana 135 and trans will be rt009513. I'd prefer a isl due to real engine brake. but the isl 370-400hp are harder to find around here.., lots of 8.3s. I drive a Ford 8000 dump tandem truck for a friend occasionally. It runs a 8.3 and 8ll, with 4.11 44k rears.. it pulls like a tank, top end and hills are limited, but it has pulled 20 tons in the box. it runs same loaded or empty. In a light truck with the right rears and trans you should be steady. The was a old conversion from about 10 -15 years ago in the TDR where the guy did a 8.3L in Superduty I believe it was a OBS. It ran good but he said it ate more fuel, and took longer to warm up and run clean in cold weather to to the light load on the engine. He had to cut fire wall and do body lift etc.
You may be able to do a search and dig up pictures etc. I had saved them to my computer but it had since crashed, losing the pictures etc.
Thanks,
Deo