DRRfanatic425-
I have a few DRR modified with Li Ion batteries (8.4 peak voltage), but I am only running modified 180 motors. As of yet there have been no failures and no burnout on my ESC.
Your big block most likely draws more current and in that case you may be at risk. Plus, it may draw more than is "Good" for Li Ion batteries. You will need to consult a Li Ion expert on that. I have heard they are good for up to 280 motors (don't know if your motor is this size or larger).
As far as your current battery pack, your capacity is 800maH. Your voltage is additive in you pack (end to end battery stack - serial). To have additive capacity, you would need to run twin 800maH packs in parallel. In that case you would have a capacity of 1600maH.
As far as foams, I know where to get foams that fit, but cannot confirm larger diameter foams. Email me if you would like to discuss where I get DRR parts.
You car sounds wicked fast. Enjoy. I really have a blast with these cars, and I see you do too.
Regards,
Kyle Lucas
kydawg1@yahoo.com