Measure the bell again. It should be either a 4.354" or 4.805"
If it's a 4.354" you can machine the bellhousing out to 4.805" and run this bearing retainer
https://www.summitracing.com/parts/dcc-4529696. If it's 4.805" you can just run that bearing retainer. Either that or you need to find a new bellhousing.
The 4.354" retainer bellhousings can't be opened up all the way out to 5.125", 4.805" is as far as they'll go. Likewise, you can't put a bearing retainer with an outer diameter of 4.354" on an OD or later 308 input bearing transmission because the bolt circle for the bearing retainer is 4.16" on those, the transmissions that original had 4.354" diameter bearing retainers had a 307 bearing and a 3.7" bolt pattern. If you have a 5.125" bearing retainer on there now you have the 4.16" bolt circle.
