Only the 1973 340 was externally balanced as far as the LA engines go. All the rest were internal. Also, there are plenty of converters well below 1800 stall speed, such as trucks. I've seen as low as 1100. So I don't know where "that" came from.
A lockup converter is for a later model transmission designed to work with the lockup converter. They do exactly what the name implies. They lock completely up like an engaged clutch at a certain speed. The benefit of this is, it acts like another gear and lowers engine RPM for greater mileage on the highway through reduced engine RPM. Unless you have a lockup transmission, leave the lockup converter alone. It will not work with a standard non lockup transmission, such as the regular three speed 904.
Also, yes, there are plenty of converters under your 350 dollar mark, however, you need to keep in mind one thing. As the price of the converter gets cheaper, the quality also gets more poor. COnverter technology has come a very long way in just a few short years. Used to be if you wanted say, a 3500 converter, you had to put up with a lot of slippage "up to" around 3500 RPM where the converter finally locked up. Now, you can get a 5000 RPM stall converter that's tight enough to drive on the street and still not slip a great amount, but will still flash to 5000 RPM on an all out launch. Of course, you'll not want a 5000 stall. My point in all this is, regardless of how tempting a cheapass converter is, don't do it. You'll regret it. The converter is the single most important part of an automatic equipped car. It can make or break your entire build. I recommend spending between 350 and 450 on one. You can call a good converter company and tell them what you have and they will build you a custom converter to match your vehicle. Precision of New Hampton is one good company to work with.
