That's really interesting. Your dad's drive-train seems to be very similar to my Duster's drive-train. The 340 in mine was built about 4-5 years ago, with a Eagle 4 inch crank, and .040 Icon forged pistons, Scat I beam rods, = 418 CI. I believe my compression is just under your dad's engine at 10.1-1.
The builder used the factory J heads, but they are fully ported/polished, with stainless 2.02 intake/1.60 valves, and Indy roller rockers. Camshaft is a solid unit, from Bullet Racing .... 248 deg. duration @.050. IMHO the cam could be a little larger with more duration, but, it's only a street car! Intake is a Victor 340 that's ported/polished too, and a Demon 850 cfm carb up top. Summit electric fuel pump with braided 3/8" lines throughout. I use 91 unleaded ( no ethanol) from the local elavator station.

My trans is a forward pattern MVB 727, and a 3200 stall convertor,with a 4.10 gear in the 8-3/4. Mickey Thompson Sportsman Pro 26X10.50" tires.
Don't know what brand headers... Hedman maybe..not sure? 3 inch exhaust to rear bumper. The guy I bought it from, told me the Duster should be
an easy high 11 second car...but I don't want to take it to a track until get some frame connectors welded in first. And a drive-shaft loop as well. My Duster pulls really well too, Have not taken it to the local track, as of yet though.
What are the specs on those Pro-Maxx heads your'e using??