ccperf721p,
You beat me too it, we must have been typing at the same time,
Shaft rockers are also different some take .250 offset intake rockers, requiring a .180 or .200 offset intake roller lifters. I've got a set of Brodix 10's RP,FP's 23* spredports that take the .250 offset rockers and lifters. I bought the T&D rocker from Randy Roberts with the mud truck, that he had on his 18* heads. I'm not sure that all 18* heads require the use of offset lifters. I think this engine will make about 750 HP with injection on alcohol.
I've got a set of Lemon 2"X2 1/8" with 4" collectors that are Malibu specific, but they weren't cheap by any means.
JMO
Zip.