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I recently picked up the models needed for this army, plus I have an assault sqaud I'm not yet using.
Six Marine Tactical Squad A
Sergeant With Terminator Honors
Six Marine Tactical Squad B
The idea was to have the jump pack Chaplain move down fast on one side, and Squad A in the Razorback move fast down the other. All while Squad B moves forward centrally, backing them up. The Chaplain and Sergeant pack a punch in close combat for HQ killing, and the Razorback is added fire support. Would some grenades help my cause, how about replacing something with an assualt squad? I've not played 40k before, so this is all in theory, based on the little I've picked up so far. I don't REALLY know what I'm talking about yet, so feel free to give constructive criticism.
First, tactics. Running the chaplain down a flank on his own isn't the best idea. Better have him skulk behind the razorback.
Also, there are foes who advance on you and who you want to gun down as much as possible before they reach you. In those cases you can simply wait for them.
Then the list. I'd dump some of the chaplain's wargear to give him frag grenades and to give the Razorback extra armour.
You also don't need such a kitted out chaplain in such small games but there isn't much you can expand on the existing units with points freed on him.
Another, inviting, alternative is adding another small unit. An Assault squad or, as I think you got the models left for it, a Tactical squad. Either unit would cost you some 100-110 pts so you'll have to save a lot.
By taking only a very cheap Reclusiarch chaplain (frags, pistol and jump pack only) you can save some 50 pts. Build the Razorback with heavy bolters instead of lascannons (the squad with lascannon provides enough anti-armour) you'll save another 20. To free up the rest of the points you'd have to undress both units.
So it is stretching the army but the extra unit could be a big help.