Advance Adapters is the company that makes the adapter plates. I haven't really looked that much for 4BT's, but the ones I did see for sale were I think $1,700 for the cheapest and then like 7 or 8 grand for a rebuilt one on eBay.

Another thing I forgot is to check out 4btswaps.com for a ton of info on almost anything you need for the Cummins swap or even some other diesel engine swaps.

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1996 Ford Ranger STX 4x4 4.0L
1983 Honda Shadow VT750C