G'day Ken,
Yep, it's the right one.
The Master Parts Catalogue (20 Years of Holden Production) lists the part number for extension housings assemblies for FX-EK Holden as 7408347. This assembly is the housing and bushings made up with the alloy casting. The alloy extension housings have either 7408348 cast into them (one number higher than the parts list
as this is a casting, not an assembly), or just plain “HOLDEN” and no part number. The dimensions (overall length, bushing length and diameter, bolt location, locating flange lip diameter) are identical, through the mild steel unit is 3/16” longer due to the use of an extra shroud at the rear of the extension. A lip seal is press fitted into the rear of the extension and seals up against the main drive shaft as it exits the gearbox. The two units, including the seals, are fully interchangeable.
This may help:
FB/EK Holden 3-speed Crashbox Enthusiasts GuideCheers,
Harv (deputy apprentice crashbox fiddler).