Im a Proud owner of a set of stepped 1 3/4" to 1 7/8" Dynatech Headers on a 71' Nova SBC 406ci , that being said Ive had a few different sets of quality brands names (Hooker & Dougs with 1 5/8" pri- 3" collect) on a prior 355ci SBC 425-450hp , Now running the 406 with bout 500hp the stepped header was a must ! Now the Fitment & Craftsmenship and finally not havin to make adjustments or touching of the Big three I have to go with Dynatech's hands down ! They fit like a glove with no ISSUES for me and cant say that for the others ! As for the size of the Primarys for your motor only Dyno wil tell you what your engine likes better @ cruising or high speeds ! But keep in mind If make power upgrade changes later then your Motor will thank you for the Bigger set of course !