Maximum distance I can move batteries from alternator?

I have a 250amp alternator in my ford pickup and just bought 2 new 1320CCA batteries to replace the smaller 600CA batteries, but they are too tall and the hood will hit them. I want to put them in the box of my truck. I have a '91 diesel so I need 2 batteries, and I'm just wondering if moving the batteries so far from the alternator will minimize the charging or damage the alternator. Please don't answer this with "I think" or "maybe"
I'm looking for facts not opinions please.

It won't be any problem at all for the alternator, charging current is relatively low compared to what's required by the starter. Make sure you have some big beefy cable going to that.

Yes you can, but you'll need 0000 AWG cable because of the voltage drop. And you should run both pos and neg cable. Don't use body ground for neg. Run the cable under the truck but enclose it in plastic conduit (blue smurf tube) to prevent short to ground and prevent damage from rocks and punctures.