Crossflow questions for you old timers

Joined
Aug 31, 2009
Location
Murray, KY
#1
I've read a ton on the old crossflows. Here's what I gathered. There were two types. Bubble back and flat back. My 85 150 is a flat back. I've read that all the 2.5 power heads were pretty darn close to being the same and in order to make more power they changed carbs and timing. What about model designations like "gt". Mine doesn't say gt anywhere. Any input would be nice. And what are the "safe" operating wot rpms?