I almost never use 6th in my T56. I found it on CL and then had it rebuilt by a race shop, its good for 700hp or so.  
 But the fit is tight, i did'nt tunnel, but have a high speed vibration i haven't been able to find or fix, but that is for 90+. 
 On the track i've had it up to 126/128 ish, in 4th with 3:73's, 6500rpm, didn't have enough track for 5th. If i had it to do over, i'da looked more into a TKO500 or 600(can't remember the difference between the two.) 
 Or look into Hurst Driveline conversions (?), i would def go that route for the total package. After doing my whole t-56 conversion, the price was the same as their's but without the driveshaft! 
 
anyways, just my 2 cents. Enjoyed watching your build...mike
		 
		
		
		
		
		
		
			
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				Mike
			 
		
		
		
		
		
	
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