4btswaps is a good place for info.
i have been around one or two of these and performed the swap myself in a 92ish jeep cherokee. the shake is mostly at shutdown and if you are idling in gear with an auto. they they can shake pretty good. driving down the road, they are nice and smooth.
transmission choices are pretty wide open. they came with GM transmissions both manual and auto. they came with ford transmissions behind them as well. any adapter plate that was used on a 6BT can be used on a 4bt. that opens up all of the dodge diesel transmissions to you and any of the SAE pattern transmissions that were behind them in industrial applications.
Destroked is a company that makes a bunch of different flywheel housing/adapter plates that opens up a bunch of other options as well. they have a GM standard bell pattern adapter that takes the tilt out of the OEM ones that step van engines had as well.
i wouldnt be scared to put one in anything that a 6bt wouldnt fit in.