I'm sure your six pack pistons have the standard 5/15,5/16, 3/16 ring pack piston grooves, make sure though , and then order a set of rings for a motor home motor in the proper bore size if your piston top are thick enough to use in that motor for your deal
The TRW should have the needed piston to cylinder wall clearances built into them, you might want to add another .0010 to be safe though
Take one of those pistons and measure it where you should on the skirts at room temps and then stick it in a preheated oven a little over 250F and remeasure it to see how much it grows at those temps. , be careful so you don't burn your fingers also
On the 440-3 motors they are no where near like the 361 and 413 industrial motors so don't count on finding any 440 or 440-3 motor with those early heads and water pump timing cover like those on the early, pre 1973 H.D. 361/413 motors.
As far as the 440-3 valves I'm not sure about them or how they where made