This is data compiled by CentralCoaster. It lists all the bolt sizes for a stock L98 intake manifold and some of the attachments.
These are commonly replaced with allen head bolts and are easier to remove.
TB = (4) M8x70
Throttle bracket = (3) M6x12
Distributor cover & TB plate = (9) M4x12
Intake base = (12) 3/8-16x1"
L98 Tstat = (2) 3/8-16x1.25"
EGR = (2) 5/16-18x1"
Perimeter VC's = (8) 1/4-20x1"
centerbolt VC's = (8) 1/4-20x3.5"
Top of runners into plenum:
plus the special bolt with throttle cable holder.
Bottom of runners into intake baseplate:
(4) M8x55 underneath each runner pair between tubes.
(6) M8x30 at each end of the runner flange, and one in the middle
(2) M8x40 go into the backside of the runner flange, you have to do these from the opposite side of the motor.
(4) M8x35 bolts from the top
(2) M8x20 on the little flange in front of the intake.