I am going to upgrade my battery cables from 2awg to 2/0. The old cable ran from my battery in the trunk under the car up to the starter. It snaked around suspension parts through and over frame connectors and was tight in places so running the 2/0 in the same path doesn't seem possible. I would rather run the cable through the trunk along the left sill under the carpet and through the firewall to the starter. Is it ok to run the cable through the interior?

Mine is in the interior. I don't know if it's legal, but that's where it is!

I will assume you are asking if its legal... yes it is

One more thing.....now I have the engine grounded to the frame in the front and the battery grounded to the frame in the rear. Is that ok or do I need to run a negative from the battery up to the engine?

I weld a stud to the frame... front and rear and use
that as the ground.... then run a ground to the engine
besides using the motor plate

Mine run through the interior, following the factory harness route along the left side. Perfectly legal. Just make sure to use grommets or a short length of rubber hose at possible chafe points.
Short ground at the back and one at the front are fine, no need for a full-length neg cable.

Great thanks. I hope to have the new cables this week to install over the weekend. Hopefully they eliminate the hot start issues.

If you have a uni -body, use your old #2 wire as the new ground from rear to front on the engine, you will notice the difference in starting

Good idea using the old #2 cable as a separate front to back ground. Why didnt i think of that? Right now I have a ground from a starter bolt to the frame in the front. I have a second ground from the battery in the back down through the trunk floor and boltedthe the frame rail below. Could I just run the front to back ground from a motor mount up the right side and bolted the the frame using the same bolt that the battery ground strap attaches at? Or would it need to run up to the negative battery post doing away with the short battery ground?

look at the battery cable system that spaghetti menders sell

I will say that the negative side of your typical race car is usually sub par, when really it needs to be just as good or better than the positive. Considering the negative side of the battery is what really is Hot, and provides the flow of electrons.
In reality the whole frame is energized waiting to jump on the starter, fuel pump, fan what ever when the circuit is closed
They figured this out in the 40's and 50's but didnt want to change the standard system and battery around, causing more trouble and confusion.. but when it boils down it works the same way, but this is why the ground side needs as much attention as the hot side.

I have two ground wires from my engine block to the frame rail. One on each side. Then I have a 2ga. ground wire from the battery to the rear frame rail. If it isn't grounded well enough you will find out. Just try to start the car at night w/o any lights on. Any where you have a really close metal/metal point you could see sparks. Don't ask me how I know. My brother pointed this out to me one evening when he was visiting. I was getting an arc between my one header pipe and the inner fender. Not good. Put another heavier ground on the block and took care of that. Starter spins much faster now also.

Also go to NAPA and get a heavy duty fuse to put in your positive wire. I have a 300A fuse in mine. Yes it will still do some welding if the wire gets cut, but not as long as it would if it were not fused.

Is the 300amp fuse something I need to get professionally installed in the line or does it bolt on one end? Any one have a link to one online?

Here are some alternate points of view as to how you might perform your trunk mounted battery wiring - see the diagram at the bottom:

http://www.madelectrical.com/catalog/tm-1.shtml

BTW, I run my cables inside the car under the sill plates to the fireweall and then out to the starter or starter relay

So I would take the line from my battery positive and bolt the lug end to the 300 amp fuse and then bolt the fuse to the post on the kill switch? Its that simple? The pic I saw on napa website looks like a fuse in middle with lugs to bolt to on each end. Is that the right one?