Here's the one that I put on the 390 in the Swinger. I tried to insert the link to Summit's web page but I couldn't get it to work so I just copied the page. This one is SFI Rated for $180. They have a non-SFI version for about $50.00 less:
Pioneer Automotive 872037 $179.95
Estimated Ship Date: Today
Brand: Pioneer Automotive
Product Line: Pioneer Race Balancers
Part Type: Harmonic Balancers
Part Number: PIO-872037
Engine Balance: Internal
Balance Style: Neutral
Safety Rating: SFI 18.1
Degree Markings: Yes
Outside Diameter (in): 7.240 in.
Harmonic Balancer Material: Nodular iron
Harmonic Balancer Construction: Elastomer
Harmonic Balancer Finish: Black painted
Mounting Hardware Included: No
Quantity: Sold individually.
Notes: Weight is 9.40 lbs.
Harmonic Balancer, Race, Internal Balance, 7.24 in., Iron, Black, Chrysler/Dodge/Plymouth, 318/340, Each
Check to make sure this part fits your application
Lightweight, SFI-approved race balancers.
These Pioneer race balancers bring the advantages of bonded rubber to high-revving race and street/race applications where an SFI-approved balancer is required. Each balancer features a precision CNC-machined AUSI 1045 steel center bonded to an equally strong steel inertia ring. The advanced design makes these balancers very lightweight for an all-steel product. The steel inertia ring on these models is positively protected against forward and backward movement and has the added assurance of bonded rubber to eliminate spinning. Every Pioneer race balancer features easy-to-read, computer-etched timing marks.
Ray