How good of a driver are you? Lack of power can be a problem but if you're driving skills are on par with the guys you're loosing to, then more power is not your answer.
Here's a bell housing that will work for you. Maybe this will keep you from having to make any transmission changes beyond the flywheel and clutch. I don't know the Viper T56 though.
http://lakewoodindustries.com/drivet...dge-viper.html
Honestly, it sounds to me like you need to just go ahead and make the change to LSx. You have a lot of changes you're going to need to make to get an SBC competitive power wise. Many of these same changes will be needed with the LSx swap as well. I think you'd be wasting money to build the SBC and then swap to an LSx. The other thing to realize is you're scratching the surface of the LSx at those power levels. With the SBC, you're starting to get into very expensive territory to make even more power. Long term investment points towards LSx in my opinion.
For what it's worth, I'm telling you this as someone who intends to build an LTx motor. Call me crazy for not following my own advice but I'm not racing anyone either. Make the swap or buy Beach Cruiser's 377 he has for sale.