After reading one of my old Shelby Americans it stated that the R model GT350's used ported heads with larger valves, different cam, some engines got 4 bolt mains added. They used baffled oil pans and had external oil coolers too. It does not specify 350 HP but I'm sure the R models approached that in that state of tune.

The little 289 was abandoned for the GT40 LeMans cars after '65 because they would crack/break their main journals before the 24 hours were met. The cross bolted 427 had no such dilemma and in '66 they handed a win to Ford ( actually a 1-2-3 finish)

______________________________________
Stu

1967 Mustang Coupe

1964 Mercury Park Lane Breezeway