5.0L HO Swap w/o EFI by Darryl Lang
A few very important things must be changed to swap a newer 5.0L HO motor
into a Mustang II.
The 5.0L HO uses a 50oz imbalance instead of 28oz imbalance for it's
You must have the flywheel or flexplate balanced for a 50oz imbalance
instead of the stock 28oz imbalance.
You could use a newer flywheel or flexplate, but the bellhousing must
match. The Mustang II bellhousing is smaller diameter than most
bell housings and requires a special sized flywheel and flexplate.
B&M has a correctly sized flexplate available with the 50oz
The 5.0L HO has a Roller cam made of billet steel instead of cast
iron. You must use a steel or bronze distributor gear with the roller
cam. The stock Mustang II distributor has a cast gear.
If you're going to use EFI, the stock distributor already has a
0.531" inside diameter steel gear.
The Mustang II distributor for DuraSpark uses a 0.467" inside
diameter distributor gear. Aftermarket bronze or steel gears are
available from Mallory and MSD.
The '82 DuraSpark distributor will fit a 0.531" inside diameter
distributor gear so you you can use the stock replacement gear
from a roller cammed 5.0L HO
The 5.0L HO aluminum valve covers can be used:
To clear the Mustang II air cleaner snorkel, they must be installed on
the opposite sides from stock so the oil filler neck will not be in the
The PCV hookup is only 3/8" instead of the normal 1/2" so
either a hose adapter must be used, or a PCV valve from a different
application. I used an '80s Nissan screw-in PCV valve, screwed
directly into the intake manifold with a 3/8" hose from the valve
to the oil filler neck.
The crankcase must also have a free flowing vent. The EFI intake
has a large vent from the crankcase so it doesn't have any vents in the
valve covers. To resolve this you need to replace the oil filler
cap with a screw on K&N breather.
The 5.0L HO uses a serpentine belt system. If you want to retain the
Mustang II belts and accessories, the water pump must be replaced with an
older non-serpentine water pump because the serpentine water pump spins
The 5.0L HO uses a 351W firing order. Change the firing order to
If you plan on leaving the Mustang II air pump installed, it bolts
directly on. If you want to remove it, install two 1/2" plugs in
the air port inlets at the back of the heads.
The 5.0L HO uses an electric fuel pump so there is no fuel pump eccentric
or fuel pump mount in the front cover. Either swap the eccentric and
front cover from an older 302, or switch to an electric fuel pump.
The 5.0L HO uses a dual hump, rear sump oil pan that will not fit in a
If you're using a Mustang II bell housing, a Mustang II oil pan will
need to be used, otherwise any front sump pan will fit.
The dipstick needs to be moved to the front of the motor. The
5.0L front cover would need drilled to accept the dipstick, or an older
302 front cover will already have the dipstick hole. Don't forget
to plug the dipstick hole in the block.