wowee that is a lot of work to do 4x
no water restrictions in Stock mach 1s
there is an vacuum valve in the inlet line only if you have AC but it just closes the water flow to the HC when the AC is on
what brand HC are you using. I used Modine back in 96 and thank god its still going.
I do a flush every 2-3 years about 1500 miles
you can try a water restrictor from a 91-93 GT. it will fit in the 5/8th hose and you can give that a shot.
cheap enough insurance anyways
or you can use a 5/8th brass petcock valve in the inlet line and just keep it half open.
1970 Mach 1 San Jose built Dec 23 1969. Marti 1 of 7. Purchased in 1987. Original family owner of the power train
351C 2v FMX.
1993 GT 13,000 miles, Built 2-12-93 Bought 8/3/93 Auto, 3:27 Axle, cloth, sunroof, AC. Unmolested all original car. Purchased new 8-3-93. still has the factory windshield fluid.