This is my $3000 recommendation, and how I would do it again...
1. Find a really nice 70-72 duster, all-original, interior intact, straight, nice grill, slant six automatic car, for $2000-$2500
2. Find an original 73-76 four door whatever a-body with 318/auto/big bolt pattern rear (preferably 8.25, but a 7.25 gets you on the road), power steering, disc brakes, the works... score this for $500-$1000.... (sell off grill/bumpers/fenders to the guys needed them for their late-A bodies)
3. Get the Mopar Performance chassis manual from Mancini $30
4. Spend 3-4 months cleaning, painting, and combining everything from the 4-door into your new sweet *** duster
5. Drive as you score a 360 and a good rear, if you don't already have an 8.25 diff in there from the swap. To answer your question, the 904 is better for a street small block rocket; the sb 727's are good for towing and robbing a lil horsepower.
wow you could have read my mind a few years ago. i wanted to get back into doing an old skool mopar B body like i used to back in the 80s and 90s before my stint with turbo mopars. wasnt sure which way i wanted to go. A, B, or E body all are cool. i just happened across a 1974 Dodge Dirt more door complete in Gator Green inside and out. sure it was ugly as sin, but it was BBP, power disc brakes, power steering ,and V8. it was an A/C car but all that was stripped out by a PO, plus it had a solid floor pan, and zero body rot. i scored it in running condition at my local police auction for $400.
i kept the car parked at home and left it complete. well now that i just bought a donor car it settled the decision i was going to build an A body LOL. now to narrow the choices down to 67 to 72 as im not a fan of 73 up sheetmetal on A bodies. lots of darts out there, lots of dusters too. dont like the scamps, sooo old barracuda or a demon. found out the 67 notchback coupes are pretty light weight at 2,700 pounds. score a 67 from my salvage yard buddy complete for $1,000. all i wanted from this thing was the body shell, and the clutch pedal setup. perfect its a slant six car, 3 speed manual on the column, bench seat, manual steering, manual brakes, no option nothing except for a factory vaccuum gage and trip odometer.
now to drag my buddies flatbed trailer to my house, strip out the dart for everything i need for my project, strip out everything from the dart i can resell, sawsall the center of the body out of it for the floorpan and transmission main crossmember. load up the pile o dart onto the scrap trailer. now dissassemble the cuda and relieve it of all its slant six parts, and pile all that onto the scrap trailer, except for the pieces i could easily resell.
drive the pile o dart and slant six parts to local scrap yard when steel got high. score get paid $200 for the scrap metal. now im only into my project $1,200. sell off dart hood, and fender $250, trunklid $75 taillights $25. only into the car for $850. get $150 for tranny as im going 4 speed only into it for $700. i ended up selling enough stuff i pulled from both cars i didnt need that the parts i kept from the dart to use, plus the cuda body i bought to put everything in i was into for $0. then i started to have to buy stuff for the project. im into it for $1500 to $1800 now.
if ya got the room at your property to do it this way then id recommmend it. saved me a lot of dough.
matt