If Thunderbikes takes off then a 1000ss motor might be going in the chassis.

Even then with a 4lb/bhp limit I am not sure that will be needed.
1080cc overbore on a 1000ss will not be necessary imo - the best SV's are chucking out 84bhp atm. I've got my 800ss up to a tad under 80 with very little effort - 85 should be in reach with a full system and some other tweaks. If a 1000ss responds in the same way then I should think 95-100bhp is easily attainable without actually having to do anything significant.
We shall see. I am doing some track testing next month...hopefully.