Need information on 340 J heads

The letter head series. X,J,O,U etc... are factory iron heads that came on 340 and 360 engines. The only performance head is the T/A head and the early 340 head, both with 2.02/1.60 valves as stock equipment. A 2.02 can be added to any letter head or head there after.

In stock form, there fine at best for daily drivers and mild cam's added into the engine. Of course, other performance parts added on help, but, back to the head issue.

They flow on ethier side of 200 cfm on the intake.
They can be ported out quite well and flow up to 270 cfm, more is possible.
These heads are priced well and even better if the work is done right.