I think I can help, I have a 108 with a 38 inch deck, but my mule drive is for a 44,50 inch deck and my subframe is from an older cub, for a 38, 42, 48 deck. The subframes you have look like a 44,50 inch deck subframe (in the back) and a 38 inch deck subframe (in front). They look like the correct subframes for a 108. So you don't have a 42 inch deck subframe. So you can either get a 44 inch deck, or find the correct subframe. Also, I think you can remove the extension your father made for the forked piece. You'll have to doublecheck, but I bet the fork goes over the lift handle shaft, and not the platform support shaft. The lift handle shaft is closer to the front of the tractor. I got all my information from the Technical Library, Implements section of the website. An illustration of the 38 inch subframe is on pages 15,16 of the IH 38-44-50 Mower Deck Manual. And there's an illustration of the 44,50 inch subframe on pages 19,20 of the same Manual. Hope that helps.
