Selection of Torque Converter and Rear Gears for Hot 340

JMO, get the tune up at idle correct before delving in much further. Disconnect hose at vacuum advance can and plug it if it has Vac Adv. Get a vacuum gauge and timing light. Hook up vacuum gauge and get a reading now. Set the timing and find the point where the engine kicks back or cranks very hard on the starter when warmed up. That's your idle timing limit. Then set the timing a little below 2-4*, reset idle speed, mixture screws and check vacuum reading. The vacuum reading and initial timing will likely help determine the camshaft in the engine. You want to get this correct because EVERYTHING above idle is a band aid if the foundation (idle) is poor.

Check total number and make sure it's not to high with vacuum advance disconnected and plugged. DO NOT pick an RPM to stop, rev it up until it stops advancing. See "hillbilly timing tape" if your balancer isn't marked. Usually total #'s fall in the 34-38 on a SB with iron heads. If it's too high you need to bust open the distributor and limit the advance.

It takes work to get this right. Some distributors are easier to work on then others. MSD are simple and I have bushings that make this process easier.

Converters are the KEY to a auto trans car. 340's like flash speed! 3.55 and high #'s are good too!

Don't feel bad, I have a car just like yours. Someone else built a 340 with a 508 cam, 3.21 gears and a stockish converter. A granny in a walker can outrun that thing to 30mph. Sounds like tarzan, runs like a crippled Jane. LOL