There are several variables.

Depending on whose stuff you use. Whether you want starter shims or not.

Originally mopar had the starter ring on converter. With JW wheel you have a crank adapter that spaces the flexplate out for proper converter clearance. By doing this the starter ring is closer to block requiring starter shims. They did not know how thick you needed due to midplates or not and sent a stack.

ATI makes their bell with their flexplate and crank spacer that also provides the 1.705" converter pilot.

REID made their bells in the beginning and offered flex plates with their sokution requiring no starter spacers. Customers switching from JW kits complained about the longer length so REID updated their bell shorter.

Their is two common ways to do this.

Use JW wheel and crank adapter with Reid bell then use JW starter shims.(I'm not in favor of this because it's a bandaid) A lot of big converter companies recommend this.

Use a standard a direct bolt in flexplate order converter with a larger mopar pilot or mopar to gm adapter and add JW starter shims.

With a 1/4" midplate covering starter pocket with Reid bell with the correct flexplate adapter you can use a standard height gm converter and everything fits.

I just removed a JW bell and trans. Installed Reid bell and trans. Used customers JW wheel and remade his crank adapter and a off the shelf standard height gm converter fits with .140" endplay.

So no REID's don't just bolt right up. ATI does, JW with the right combo of starter shims, and REID with the correct flexplate, crank spacer and starter spacer. I hate starter spacers so I have my way of accomplishing spacing that is just like my bellhousing kits for R5 nascar engines. But, you call your converter guy and tell him you have a midplate and you are screwed.

ATI and Reid are both great sources for bellhousings. BTE and QuickTime use Reid transmission patterns so I chose Reid when designing the R5 to aftermarket case. ATI T400 has both ati and reid boltpattern, for information.