Last month, we began the buildup of what is certainly the most overlooked of all the Chrysler Hemis-a 331 with the extended bellhousing. Made from '51-53, these engines have been pretty much ignored, which means they are usually cheap as far as Hemis go. The larger 354 and 392 certainly have more performance potential-and the long-block extension can be an issue when adapting a contemporary automatic transmission-but we're building a driver, so the smaller displacement isn't an issue. The extended bellhousing actually works great with a simple flat adapter that will allow us to bolt up the four-speed transmission we want to use, and we got the engine for next to nothing-this was the Hemi for us.
Last month, we followed along as John Beck at Pro Machine assembled the short-block. This time around, we're going to look at the finishing details and some of the special features of these engines.
Rockers/Pushrods
Chryslers used a variety of pushrod lengths in Hemis
'51-53 intake 8.4375-inch / exhaust 9.906-inch
'54-56 intake 9.625-inch / exhaust 11.125-inch
'55-56 300 intake 9.775-inch / exhaust 11.240-inch
'57-58 intake 10.125-inch / exhaust 11.600-inch
'57-58 300 intake 10.240-inch / exhaust 11.740-inch
The use of later Mopar hydraulic lifters is one of the parts substitutions that is often made in early Hemis. While the diameter is correct, they are .085-inch longer and the pushrod cups accept 5/16-inch tips rather than the stock 1/4-inch, all of which means custom-length pushrods are required. But, in general, adjustable pushrods are a good idea if adjustable rockers aren't used. Decked blocks, milled heads, and reground cams can all impact rocker-arm geometry, and adjustable pushrods can compensate for them.
Diameter is another consideration in addition to length when substituting pushrods. Larger-than-stock-diameter pushrods will require drilling oversize holes in the head.
There are basically three choices when it comes to rocker arms: stock non-adjustable, factory adjustable, or aftermarket adjustable rollers like those from Hot Heads. We had a good set of non-adjustables so we had them rebuilt with new shafts and bushed rockers.
Intake Manifold/Plumbing
Out of all the options available, we chose Hot Heads single four-barrel manifold and topped it off with a Barry Grant Road Demon carburetor.
As with most aftermarket manifolds, this one is the '55-and-later style, which means there is no water passage/thermostat housing in front, as it is designed for heads with outlets in the front. The answer here it to install water lines in the tapped holes that align with the water jackets between cylinders 1 and 3, and 2 and 4.
Intermediate Shaft/Ignition
Unlike many engines that use a distributor with a gear on the bottom to drive the oil pump, Chryslers use an intermediate shaft with a gear attached to drive the oil pump and the distributor. There are only three shafts for all Hemis in stock applications: one for short-deck 331/354 engines-most DeSotos and all Dodges (PN 1323369); the second is for tall-deck 392 Chryslers (PN 1732823); and the third is for '57 DeSotos (PN 1732828).
In addition to stock dimension shafts, Hot Heads has custom lengths available to allow the use of a variety of distributors, including the late-Mopar electronic style. The combination we used included a stock shaft and an MSD ready-to-run distributor.
There aren't many options for mounting accessories on early Hemi heads. We enlarged the original 5/16-inch hole in the right-side head, drilled a second, tapped both 3/8-16, and then installed a pair of studs. The alternator mount was made from 1/2-inch aluminum, and an additional steel strap was added for support. | 
The alternator tensioner was made from tubing and two rod ends. It attaches to a homemade angle iron bracket that also mounts a remote thermostat housing; a pair of -10 braided lines connect it to outlets in the intake manifold. | 
Hot Heads offers a number of mounts for installing a modern spin-on filter; we chose the 90-degree style. |
These are intermediate shafts that drive the oil pump. Lengths may vary depending on the distributor used. Our MSD requires a stock '51-56 shaft. | 
We opted for an MSD Pro-Billet, ready-to-run distributor for a hassle-free ignition system. PN 8391 is a drop-in for 331-354 low-deck Chryslers (PN 8389 is for 392s). | 
We mounted a pair of Moon breathers on the Hot Heads rocker covers to make a PCV system. The top of the breather was blocked off on the right rocker cover. |