[BVR421]

rough way to try to make power with the common 63 heads, fully worked they flow about the same as a stock 67up Dport. I think you should go with modern heads and disguise them. The 63 SD heads used a different long branch, like a cast tri wye. Iron, aluminum and stamped were available back then. It has a different bolt pattern on the center ex ports. The SD center ports were spaced apart a little like the RA4 heads. The starter used a special nosecone to rotate the starter for clearance but for about the same price as a repro nosecone you can get a mini starter that is made for bell mount. I think you can move pretty good air thru the 127 and 980 heads but $$$$! The better running SD re-creations use the bathtub intake $$$$!
I believe the biggest cam they left the factory with was a solid lifter with the same event timing as a later 041. When the Dodges started giving them trouble at the finish line the racers swapped out that cam for a bigger over the counter ISKY and swapped the 3.90 gears for 4.56s and turned up the volume. Amazing how well they ran with heads that are laughably small by todays standards. Certainly state of the art in 62-63
stroker kit for a 389 no problem, use common Eagle kit made for a 400. Bore .060 and with the 4.25 stroke you have about 462ci? If you prefer a 421ci motor, use a cast 421/428 crank turned down to fit the 389 block. Pontiac Dude can set you up with that deal and the pistons and rods to match.
You may have to turn down the crank rear hub for the 63 flywheel but you really better get a SFI flywheel and bellhousing anyway so that shouldnt matter. There may or may not be a minor issue regarding the pilot bearing. You might as well start planning for the rear end. If it came with a stick its probably already got a 3.42? Make sure the posi unit and axles are in top shape before you drop the hammer. 3.64 gears are available again from FabCraft. They make a lot of SD/early parts.
One of the actual SD guys will respond I hope, Im just going from memory (dim)