2 modifications are required to mount a 1988 Chev Astro Van Coill over Shock
to the Late Bay Bus 1973 - 1979 -[1974 for sure]

#1 )  you need two -  8 to 10 mm wide spacers with 12mm hole in it,
I drilled out a M12x1.5  nut with 12mm drill
1 for each shock

#2 ) You need 2 - M12 x 1.5 x 95 mm long bolt for the bottom mount.
and 2 - M12 x 1.5 x 120 mm for the Top mount.
a 12mm washer with large O.D. for the outboard side of the shock.

You can see in the picture below, that my original shock had a offset
spacer in the top mounting sleeve.  That is what the spacer is used for.
If you have standard shocks, the top is 20mm narrower 

On the left is the original Coil over Load Leveler ® Shock
It has LL562  and CO5D74 near the bottom eye

On the right is a New Coil over for a 1988 Chev Astro Van Rear
It has 729086 and C00155A near the bottom eye
I ordered them from Car Quest using part number 50948
They are made by Gabriel

Notice the offset in the upper mounting eye spacer,
You need to add an 8 mm spacer to  keep
the shock from hitting the body
This spacer can be a stack of washers that are 8 - 10mm thick

The picture below shows the bottom eye

You can see the new shock is wider and requires a 10mm longer mounting bolt,,
or if your tricky, you can remove 5 mm from each side
If you try to grind them, the rubber will heat up and burn, so be careful

 get a 10 mm longer bolt
M12 x 1.5 x 85 is what came on my 1974,
so I replaced it with M12 x 1.5 x 95mm

If you presently have standard shocks... then you need 20mm longer bolts.. see #2 above

The picture below is the shock mounted on the 1974 Vw Bus.
you can see the spacer on the left top of the shock,
And the retainer washer on the outboard side of the shock

Jamie Rivers
jrivers@globalserve.net