Well that is a bummer. I haven't run into that exact problem before but I'm familiar with those types of issues. There are some options but they'll all cost money. Here is one option: https://www.holley.com/products/drivetrain/bellhousings/engine_dyno_stand/parts/77-251

Here is another option: https://www.holley.com/products/drivetrain/bellhousings/engine_dyno_stand/parts/RM-8001

I'd think that the dyno shop would be interested in having one of these universal bellhousing on hand since then they can make more money in the future by testing BB Mopar engines. Maybe split the cost with them or something.