If the OP wants a 2500 converter than that's ok. But when I see what he's doing that pops up as a big red flag. The car is heavy, has a fairly tall gear and isn't making a bunch of torque. So handicap it with no converter and then buy a cam to try and cover that up. Then it will be a ***** to get the tune up correct so it doesn't rattle its brains out trying to get it to move, and every time you get to tip in it does the same.
So you retard the timing (power loss) and then to get the rattle out at tip in you end up unplugging the vacuum advance (another power loss and the fuel mileage goes straight in the crapper) and where did the OP end up? With a confused, hard to tune, no fun to drive fuel gulping pig.