The bellhousing bolts are threaded into the block. Use the same ones.
From the 85-91 parts books. Download your own copy from my signature...
#2 Adapter to transmission;
- 11500931 Qty. 4, BOLT , HEX (M10 X 1.5 X 35 10.9 Property Class)
#4 Adapter to transfer case;
- 11513606 QTY 6, BOLT , HEX FULL THREAD (M10 X 1.5 X 35 10.9 PS)
- 11509161 Qty 6, WASHER , FLAT (10.8 X 18.54 X 1.95 ,1050, PS)
GM called out 10.9 Property class bolts. I would NOT recommend using lighter class 8.8 bolts.
There's a torque brace (#14) in the parts blowup that you don't want to leave out.
- 10 & 20 series is 14020856.
- 30 series is 14068719
You'll need the transmission to adapter seal #5 and the transfer case to adapter gasket #1 if you don't want leaks. MD8 is the RPO for the TH70R4/4L60.
- 1358899 SEAL , ADAP TO TRANS (4.318)(W/MD8 )
- 15642512 GASKET, TRFER CASE ADAP (K/V3)(W/M20) (K/V1 ,2 ,3)(W/MD8)(1989 -91)(W/MT1 )(1991) NP241-C

