Actually there is a lockup conversion that was developed about 2 years ago. It is made by a company in New York, I think, I could look it up for you if you'd like. It was developed for racing, and will handle a lot of HP (800 - 900). The only downside is that it runs in the neighborhood of about $2,700 for the parts to convert it (including the convertor), then you essentially have to rebuild the tranny to install everything (another $400 or so, depending on your tranny shop) (unless you can do your own tranny rebuilds). It was intended to lock up at the end of the 1/4 mile so you can get improved efficiency and better MPH.
The switch-pitch is a much better way to go in my opinion. You will still have to remove the tranny and essentially do a whole rebuild (the front pump has to be replaced and you have to putz with some other internals), but is much cheaper and very strong- you can buy a conversion kit from Kenne-Bell (under $200 not including convertor), and a convertor for about $450 (www.trisheld.com
. So if you add a bench rebuild from your local shop, you are in it for about $1,000. It is a wicked setup- in my daily driver, I get fabulous gas mileage and still occasionally can put about 750HP into it (although the convertor manufacturer recommends a limit of about 600HP). My convertor gives about 1800 low stall and 3000 high stall- works great for both highway cruising and for racing.
I gotta tell you, I love my switch pitch! I don't know why they aren't more popular. I can tell you, I'll never get rid of mine!
If you want more info on where to get the convertor, shoot me an email at bobcATgnttype.org.