How much hp and torque do you think my 96 z28 6 speed is making rear wheel and/or flywheel? My guess is 310hp flywheel and around 270 rear wheel.

Mods: K&N cold air intake and 2.5 inch free flowing exhaust behind the stock mainifolds.

Also would I benefit with a tune?

I would like to add headers, 160 degree thermostat, and air foil this summer.

Would I get into the low 13's with all these mods and some sticky tires?

 

I'd say your estimates are about right....yes, definitely do the tune after you get headers to get the full effect, you could probably run low 13's with just sticky tires on a bone stock M6. Consider some boxed/tubular control arms for the rear suspension, and maybe 1.6 roller rockers and you will be there for sure, if not high 12's.....4.10's are also perfect for the 6spd and among the best mods for the money.