Take some rope and run it around the pulleys like the belt. Have someone hold the tensioner then mark the rope. Take the rope out lay it straight and measure it
If you plan on running e85 you will be right at the limit of injectors for 1200whp. I think 1400cc injectors are recommended for 1000whp on e85 at stock pressure
I have ran a Mishimoto radiator for 5 years now with zero issues. A radiator can’t over cool. You have a thermostat issue or you need a thermostat with a higher temperature
You can ether purchase a longer belt or you can modify the tensioner so it can move farther. You will need a grinder to modify it. If you want to know how let me know. If you buy a longer belt you should either get a green belt or a rpm belt both are from gates