a999 modification questions

I have been doing some research into what trans i want to run and i was looking to go with a 904 for the weight and parasitic loss factors. I then read some info about the a998 and a999 transmissions, mainly about the extra apply clutches and wider band, and also the gearing for 1st and second. These are all great features, however for performance a lockup converter is not ideal without spending a good bit on one. Now some will say to find a 999 out of a dippy cop car as they are non lockup, but they arent the easiest to find.

So this all got me thinking, can you just eliminate the lockup function of the trans and have a non lockup converter made to fit the lockup trans input shaft?

Will there be any downsides to doing this?
Is there anything else i would need to do?
Has anyone else done this?

Sorry for the long winded post just trying to gather as much info as i can.

This will be going behind a 450-550 hp sb in a 2800-3000 lb car.

Thanks