As I had stated previously, I am looking into purchasing my first El Camino. I had talked to my brother in law and he says that Chevelle's and El Camino parts are inter-changable. Such as interior, console and more. Question is, "Are they?" :?

Yes he is right. There is some variations that do exist ,but for the most part everything is interchangable.

More than just Chevelle, all G-Body parts are pretty much inter-changeable.

I have found only chevelle station wagons parts are interchangeable

I have found only chevelle station wagons parts are interchangeable

That should only apply to fenders and frames after 1970 I "think"...

yeah it depends on the year exactly....if you are talking about a 3rd Gens - 1968 to 1972 (the only years I can offer some intelligent discussion about), then 68 & 69 are closer and 70 thru 72 are closer to each other.

On a 72 like mine for instance, the Chevelle and El Camino are virtually identical from the back of the front seat to the front bumper, with the exception that an Elky has a vent window in the door and Chevelles do not (because the Chevelle has more sheet metal on the roof to support the car and the door can be 'frameless' unlike Elky's)....

here is a link that will offer some help for you at least between 3rd Gen years anyway:
El Camino Body Parts Interchangability (http://www.chevelles.com/elcamino/ec_body.htm)

I know about my '86 =)(82-87) the entire front end is interchangeable from 82 onwards, doors on the 2 dr models and most of the interiors were all pretty much the same. Certain parts from Monte's and that also work. Some look a bit different, but fit anyway(door panels).

I replaced My interior with one out of a '84 Buick Regal, the compleat Dash assembly lower halfs of both door panels ,carpet and 60/40 seat.
looks good and just a little cut to fit.
I find all G body Chevy stuff hard to find in salvage yards but G body Buick,Pontiac and Olds is plentiful

I know about my '86 =)(82-87) the entire front end is interchangeable from 82 onwards, doors on the 2 dr models and most of the interiors were all pretty much the same. Certain parts from Monte's and that also work. Some look a bit different, but fit anyway(door panels).

I asked on another forum and didn't get too much response so, I'll ask here. Does anyone know, for sure, if an 87 Buick Regal or Olds Cutlass Supreme front clip is a direct bolt on for an 87 Elky? Also what model Pontiac is comparable?

I believe the Grand Prix is also a G-body.