For Donnyhammer 40k, I use the stats for weapons from the Rogue Trader book.
1. Simply use the ranges as presented. Any range modifier to hit shifts the attacker's die one type, regardless of the actual bonus or penalty. A Flamer has a +2 bonus to hit at short range and a -1 to hit at long range. In Donnyhammer 40k, a d8 Ork with a Flamer rolls a d10 at short range (wether the bonus is +1 or +2 is irrelevant, the die only shifts one step) and a d6 at long range.
2. Strength is only used against vehicles. Vehicles have one Armour Value and fall into three categories... Light/Civilian Vehicles = 9, Armoured Vehicles = 11, Tanks = 13. When shooting at vehicles, roll a d6 and add the Strength of the weapon. If you EXCEED the Armour Value, roll on the Rogue Trader Vehicle Damage Chart.
3. Damage of greater than one gives enemy characters hit a -1 on the Donnybrook Wound Chart. Again, this is ONLY -1 regardless of the actual penalty. If you want the game deadlier, you can use the damage listed as the penalty!
4. Save Modifier is exactly as Rogue Trader (use the Armour in Rogue Trader as well).
A. Close Combat - as Pistol in Donnybrook
B. Heavy - reduce movement and round down (no 1/2" mods)
C. Slow - Move or Fire
D. Following Fire - If the shooter scores a wound he may fire again (but only once).
6. Area up to 1" may hit up to d3 targets while areas above may hit d6 targets. All secondary targets must be within 2" of a nominated target and no target may be hit more than once.
So there you go. This is a rough guide for getting on. You could add more detail, but I tried to keep things quick and simple. I'll devote a few posts to this topic on my blog at some point and do a battle report using these rules.
Hope that helps.