[Byots]

Search old threads for additional discussion on this. The issue of high risers at Shelby American and in Cobras in lare part comes down to the time period examined. In the latter part of '64 and very early '65, the high riser was the only head considered for and used on (prototype, 3002, etc) the comp 427 cars as the medium rise didn't exist yet. An old pubicity shot shows a high riser 1x4 in a production comp car engine bay - probably the first car (I think 3004). The '65 homologation paperwork lists the 58mm webers, the intake manifolds for which were only made for the HR.

Around Feb '65 Ford/SA documents specify the aluminum head MR as the official "light weight" comp car engine, although if there ever was a full-blown factory team 427 effort, SA would have likely still used HR heads due to their enhanced performance. There were a handful of aluminum HR heads made that carry ASK numbers that are close to that on the aluminum 390 block (alum 427 sleeved down), these were used at least on the flip top and the initial engine in 3002. Because Ford shifted their attention to the GT40 and SA didn't receive homologation on the 427 car in '65, Ford was pushing the new MR engines and SA just installed what they received on most cars, not having any real reason to do otherwise - all comp cars went to independents.

3002 did run maybe 3 races as a "team" car, but there isn't alot of evidence as to whether HR heads were used (other than the way the car arrived at SA). For the most part, race efforts with 3002 were mostly to fine tune the handling and reliability, the standard 1x4 MR performed well in the car, so they weren't at that point much concerned with maximizing power. In fact, people involved with the cars back then remember having alot of 427 engine failures (a major reason the dry sump was developed) and the HR would just make that situation worse due to the higher rpm operating band.

So, in terms of the actual initial intentions of Shelby American, the aluminum HR head is the "factory team" piece, but what ultimately was installed in most comp cars was probably the aluminum MR head (perhaps a couple comp cars "came" with the HR). The August '65 dated big block Cobra SA Bill of Material shows something like 12 or 14 aluminum head MR engines in inventory at that time, so even those were rare, probably only around that many ended up in cars (some were likely blown up in testing).