As mentioned previously, you need to start with the engine mount. Did you get one with the airframe? If so, then you need to align your engine purchase with what you've got already; or a). get with Van's to purchase a different one, b). fabricate your own (A/C Spruce who sells "Dynafocal Engine Mount Rings & Kits").
If you create an account at Van's Store and register your aircraft with its serial number you will have access to the plans and service information online at no charge.
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With the exception of a few oddball models as well as the 0 320H series, all conical mount four cylinder Lycoming's fit the same mount and nearly all Dynafocal engines fit the same mount.