you want shorter?
I used
this one on mine and already thought 153mm was pretty short and it's a 4" OB. BTW, with a 7" barrel/RIS you could probably go with a longer IB.
Your best bet is to take your front end in and check the IB length against what you are building. I was trying to calculate lengths of a new outer barrel with a suppressor with a 590mm inner. Could have gone with either the 7" or 10.3" outer but wanted to have a part of the suppressor hidden inside the 12" JP rifles front end.