The cast 360 cranks will take a lot of abuse. Their main journals are bigger than the 340, 318, etc. cranks (forged & cast). In fact late '72-'73, the 340's had cast cranks, which required external balance weights on the damper/balancer and converter. But it was less weight than the longer stroke cast 360 required. When the 340 was discontinued at the end of 1973, the hi-po parts - intake, carb (bit bigger TQ), cam, springs, etc. were put on the 360. I don't have any performance comparisons, but the factory rated the 360-4bbl 5 more HP than the '73 340-4bbl. With 20 more cubic inches, I'm sure it was faster, even if they hadn't gone to the bigger Thermoquad. The 915 castings were also used on the T/A and AAR 340 6 packs in 1970. Same head as was cast for the new-for-1971 model year 360 2 bbl. But all they did was use better springs and machined the intake pushrod hole further away from the intake port, which allowed more porting but required the offset intake rocker arms. As for the 318, using later model 302 casting heads with closed chambers and upgrading the valve size to the 360 spec 1.88"/1.60" is suppose to be a good performance upgrade.