I have a bone stock 86 gt and I would like to know what size cam I can run without interference.  

Why do you want to install a cam in this motor?  

You would need to change your heads, exhaust, intake and you will need to convert to mass-air, which is expensive in itself.  Change out the exhuast, headers and put some new heads, and intake on it, and it should fly.  

Best bang for the buck would be to change the rear end to 3:73 gears and change out the shifter to a short throw.  

3.73's in the rear will make 1st gear of the T5 just about useless.  If you want something that can accelerate and have some top-end, I'd stay with 3.55's...or pull a 3.27 rear out of an automatic trans car.

Of course, if the 86 has an autotranny in it...then you typically need a steeper rear gear.  but really, the HO cam can support 350hp if you know how to tune and machine the breathing apparatus of the engine...  

BTW, why are you changing the cam?  So it'll idle differently?  Swap the E7 heads, or get them reworked by Ron Anderson Ford and get a three angle valve job,  get the intake extrude honed so it flows like a GT40, get an air filter system that isn't sucking hot air off the headers,  then get a good tune on the eek 4 and I think we already covered the exhaust system, to let out everything that went in...and you'll keep your idle, your emissions, yet the engine will make more HP.  Of course, then you'll need to put it to the ground...but we covered that.  

I dont have to worry about emissions.I know you can,t change the heads to anything worth while without fly cutting the pistons.The speed density is gone.It already has 4.10 gears.I'm switching from spray to a centrifugal blower,so I want a little more cam.  

only way for sure is check with clay on piston  blowers use specific cams with short duration better ask experts at cam co