40s might be a little loud inside the cabin at cruise depending on where you locate them and the size of the pipe you use.  Should be plenty of room under the floor for straight in, straight out.  You going headers or just manifolds and duals all the way back?  I put 40s on my T/A w-o cats and 3" duals all the way to the back and it had some nice rumble to it, but the mufflers were almost at the rear axle and the tips turned down at a 45° angle.

they do sit a lil low, but i have never dragged them!

i have headers on the wagon on the left, kicked out behind tires and 3" back to terminator mufflers. not too bad, a lil loud on accel though!

when i did my 76 impala wagon guy didnt want to duel it because it would hang low since there isnt alot of room except were the orginal exshaust is. so he put a flow master muffler then up to the next bigger pipe and ran it normal. had a nice little rumble but nice a quite going down the road.

ALL THE 74 AND EARLIER IMPALAS/WAGONS HAVE THE DOUBLE HUMP CROSSMEMBER, IN 75 THEY USED THE OFFSET, CONVERTOR EQUIPPED STYLE. EASILY SWAPPED. MY 72 KINGSWOOD WAGON I SOLD HAD FLOWMASTERS ON IT, SIMILAR TO THE SOUND YOU WANT, BUT THEY EXITED IN FRONT OR THE REAR TIRES, OUT THE SIDE. I WASNT FOND OF IT, BUT WHEN I LOOK AT THE 73 CUSTOM CRUISER WAGON I HAVE WITH HUGE CHROME TIPS OUT THE BACK, UNDER THE REAR BUMPER, IT LOOKS VERY HOKEY TO ME. THE ISSUE IS GOING TO BE FINDING A COMPETENT INSTALLER WHO CAN FAB IT UP, AND EITHER HOOP IT OVER THE REAR AXLE, OR OUT THE BACK AND MAKE IT LOOK RIGHT. I DONT THINK THAT HOOPING IT OVER THE REAR AXLE IS A STELLAR IDEA AS THERES ZERO CLEARANCE FOR THE PIPE AND THE FLOO PAN BACK THERE. I DID SEE A GUY ROAST HIS REAR CARPET FROM THE HEAT BECAUSE THE PIPES WERE TOO CLOSE TO THE REAR FLOOR KICK UP.... HARD CHOICE......

YOUR EXHAUST SHOP SHOULD MAKE SURE TO "FLATTEN" THE IPE THAT RUNS UNDER THE REAR AXLE THEN, AS THE FACTORY DOES SO THEY AVOID HAVING IT CRUSHED BY THE REAR AXLE GOING UP AND DOWN..

if you want the true sound out of some 40's, dump em before the axle;)

Not as bad as you think. You've got a long vehicle, on my 05 dodge half ton i had long tubes, no cats, 3" into 40's dumped and it wasnt that bad in the cab.  It sounded very good at WOT in the cab, and fairly quiet at cruising speed.

I bought Flowmaster 44s 2.5"dia. offset inlet/ centered outlet. Going to take it to work in two weeks to put on a custom 2.5" dual exhuast with an X pipe. I will be using mandrel bent elbows and TIG welding the whole system manifolds back. It is tight around the rear axel but I will get 2.5" elbows over the rear end, just desiding how the end the system in the rear.

ONLY PROBLEM I FORESEE IF HE DUMPS THEM PAST THE MUFFLERS UNDER THE WAGON IS THAT HE WILL GET GASSED OUT FROM THE FUMES COMING INTO THE INTERIOR. DID EXHAUST THAT WAY ON A 76 BUICK ESTATE WAGON AND ABOUT PASSED OUT IT WAS SO BAD, 3 DAYS LATER I WAS BACK AT THE MUFFLER SHOP AND RAN THEM BOTH OUT THE REAR........ HARD TO DRIVE WHEN YOU ARE BECOMING UNCONSCIOUS........

You makin a Time Machine out of a DeLorean!?

i have flowmaster 40s on my 86 pont. wagon and they sound great. and when it hits over drive its nice inside the drivers capartment. barely hear anything

i have flowmaster 40s on my 86 pont. wagon and they sound great. and when it hits over drive its nice inside the drivers capartment. barely hear anything