We rebuilt a lot of 440 Motorhome/ Industrial motors many LPG, CNG
here's the formula
if doing a rebuild do the stroker
If using the stock heads use the KB quench dome pistons (I helped design them) shoot for 9:1 when heavy or if towing
else wedge chamber heads with reverse dome piston to get whatever CR you want
you want tight quench .030-.035
We used Potvin/ Moon cam in the busses but best for you now would be a short Voodoo, Custom Howard or Bullet, or Mike Jones Motorhome .904 hyd
256 @.006 .305 lobe lift single pattern ok with headers, stock exhaust a little more exhaust The Jones cam has 50% more duration at .275 than the Mopar Performance 260 while being shorter on the seat
Work on the advance curve
these three thing together dropped the EGT in the busses 800 degrees
stock rockers will be fine
cheers
Those Headers should be done already...
OEM TQ works good, al DP manifold saves weight and does not help power below 3-4000- where you need it]
post up your cranking compression
if you tear it down measure deck height at all 4 corners and write it down
cheers