Is there a way that I can tell if my 69 was originally side pipes?
The rear valance does not have the cut outs for rear exhaust but I dont know if it is original or replaced.

the motor is a 300/350.

 

there should be a hanger welded to the rocker channel on each side by the doors i believe. that held up the sidepipes and you really should be able to tell if it was a sidepipe car from the backside,under the car if there were pipe holes covered up. unless they replaced both rear quarters and got a exhaust panel without the cutouts.. on my 69 they covered the holes up to put sidepipes on but if i got under the car i could see the old flange for the exhaust trim and where they glassed over the holes. i dont think small blocks had sidepipes either, i may be wrong about that though.

 

You could get the N14 side exhaust options on all corvettes regardless of the engine options. it was not available on early 69's. Here are a few ways you can tell it was a factory side exhaust car:
1. Insulation along the frame rails
2. On a straight exh car the exhaust is grounded with straps by the cross member. Those holes in the frame should be clean and not tapped on a N14 car
3.Rear quarter panels should not have cut outs and the rear exh panel should be straight on both ends.
4. On coupes N14 is written under the rear bulk head. I have seen it marked on convertibles at times under the carpeting behind the drivers side seat.
5. The front lower rocker panel area should be cut away on each side so the front of the covers will cleat.

 

1. No evidence of exhaust holes being "filled in" in the rear valence or rear quarter panel. (the panels are totally different and there is a seam between the rear valence and 1/4 panel that is not present on undercar exhaust cars).
2. Front side fenders trimmed for side exhaust clearance (this is where the headpipe portion passes from the engine compartment to join the beginning of the sidepipe tube; the fenders are trimmed directly above the headpipe for clearance).
3. Absence of the center exhaust pipe hanger and threads in holes in the frame for grounding strap attachment (obviously sidepipe cars should not have the undercar exhaust hanger, but look for threads in the holes where the hanger and straps would attach; the presence of threads would probably considered as conclusive evidence that the car was originally equipped with undercar exhaust).
4. Insulation between the frame and the body at the outer rail.
5. Rear quarter panels trimmed for side exhaust outlet (again the panel is trimmed for clearance at the very end of the sidepipe).
6. Absence of rocker panel trim tabs (these were the tabs that the rocker moldings on undercar exhaust cars attached to; obviously the sidepipe tubes and covers occupied this area so no rocker moldings were used)
7. Front of rear wheel wells cut to expose rear end of main frame rail (not sure of the exact configuration of this one).
8. Absence of weatherstripping or staple holes used to hold the weatherstripping on the front fender skirt shields. (undercar exhaust cars used the weatherstripping, sidepipe cars did not).