The restrictors for the heater hose are to keep from puking the heater core when you take it to red line between the gears.  The 5.0 is notorious for overloading the heater core.  I made restrictors for our 66 after having a 90 GT with a bad heater core and also having one crap out in the 66.   The heater still makes enough heat to run you out of the car.

Brake booster vac hose is normally 3/8" IIRC.

BB
 

Thank you both!

Bullet Bob wrote:

The 5.0 is notorious for overloading the heater core.  I made restrictors for our 66 after having a 90 GT with a bad heater core and also having one crap out in the 66.  
BB

Is that problem only with the 5 oh's, or do early small blocks suffer from it too?
 

Well...I bought my 90 GT from my brother in 09 with 154K.  My bro told me that the AC compressor had swallowed itself a few years prior and that the last time he drove it to work...about five years prior...getting on the freeway required a little throttle and that at the top of second gear the heater core puked all over the right footwell.

So I don't know.  Would that have happened if the core weren't 14 years old?  Don't know.  Butt, the restrictors shouldn't hurt, and might save you some grief, I would think.

BB
 

That would make sense.  I remember Smokey Yunick talking about accessory speed at racing speeds in his book, and a picture of a small block chevy with a water pump pulley that looked positively huge.

To my knowledge though the 5.0s never used those restrictors stock, possibly the police package cars did, because I think they had a heavy duty cooling package.

Most of the 289s/302s were 5,000RPM engines, except for the HiPo 289 and the Boss 302.  But the 5.0 would turn past 6,000RPM (factory rev limiter was 6,250).  So, IDK.  I'm planning to run one on my '89 GT because I hate changing heater cores in those cars and the 331 will easily wind to 6,500RPM.  Of course, with the amount I'll actually drive it I'd probably need to live to be 500 to tell if it made a difference