Wow, that's very ugly. Does the van have the small block Ford adapter plate? OK, here are the part numbers for the original assembly shown below. You may already have some of these but I'll list them.
1 3901935 Hex Bolts (8 required)
2 3907701 Crank Adapter
3 3908124 Wave Ring
4 3904361 Clamping Ring
5 3900665 Hex Bolts (6 required)
6 3918957 Flex Plate
These parts are also found as a kit under part FW9043. Hope your dad has a strong heart because there's nothing cheap in those parts. The flex plate is around $400 and the wave ring is in the $300 range. Hopefully the crank adapter is OK because that puppy is over $400. The clamping ring is the only cheap piece of the puzzle at around $15. One note, member Rube Bonet (Rob Bonney Fabrication) makes a replacement for the wave ring. May not be much cheaper but it's about 10 times as strong. With all that mangled mess I assume the torque converter is getting replaced too. Part of the problem could be the wrong lockup on the converter. The 4bt likes lockup around 1300 RPM where gas models are a lot higher.
That someone will be my 85 year old Dad. He had been a mechanic all his life. He can work circles around most people😌. He's not tech savvy so I'll have to show him this conversation and be his secretary😆!
There are billet flex plates available but you have to use a different adapter plate on the engine and the cost is still high. Destroked makes those parts. The small block Ford adapter plate is $795 and the billet flex plate is $625. In addition you have to use a Ford diesel 6.0 starter which they sell for $219. So that's about $1700 to make that conversion. You'd want to contact them to be sure everything matches up to your transmission. Destroked - THE Cummins Conversion Company Rob's web contact is Rob Bonney Fabrication . You can reach him by phone if you desire at 602-370-7955. He's located in Peoria, AZ.