Your engine should have HiPo heads that are factory equipped with close tolerance slots in the head to guide the pushrods and maintain rocker arm alignment. These close tolerance heads do require hardened pushrods as they contact the slot continuously during operation. Guide plates are not necessary as the narrow slot does essentially the same job. Your machinist is correct in that a 1.6 ratio roller rocker for 31/48-inch studs will fit, however, they simply bolt in using stock hardened pushrods without guide plates.
The confusion stems from the fact that Ford stopped utilizing the narrow slot design in mid 1966 and switched to a "loose fit" hole that required "rail" style rocker arms. The loose fit hole did not support the pushrod and relied on U-shaped rocker-arm tips that drop over the valve stem to maintain pushrod/rocker arm alignment. This design does not allow for a roller-rocker arm unless guide plates are installed to hold the pushrod aligned. A copy of Ford's Motorsport Performance equipment catalog illustrates this quite clearly and is available from your parts vendor or Ford at (586) 468-1356.
I question your need for roller-rocker arms, as the stock HiPo setup is quite trouble free and can handle any camshaft style, both mechanical and hydraulic. California-area vintage racers are limited to stock rockers by the rules and are running to higher rpm than a normal street driven vehicle will ever obtain.
SpeedySome time ago, I brought my '68 Mustang to a speedometer repair shop as my mileage indicator and speedometer did not work. The shop said I needed a new drive gear in the transmission. I then brought the car to the transmission shop where they installed a new drive gear and a new driven gear. However, they could not locate the seven-tooth gear I needed so instead installed an eight-tooth gear. When I got the car back, the speedometer still did not work but the mileage indicator was going backward. I then took the car back to the speedometer shop and they checked everything out and said that the drive gear was installed backward and that was why the speedometer did not work.
I then went back to the transmission shop with my invoice from the speedometer shop and told them that the drive gear was installed backward. The transmission shop says that it is impossible to install the drive gear backward, as there is a slot on the gear so it can only be installed one way.
Please let me know how I can get this fixed before I get a speeding ticket!Douglas SvenkerudWest Chester, OH
Unfortunately, the transmission shop has installed a drive gear for a unit that has the speedometer cable entrance on the opposite side of the transmission. The angle of the teeth on the drive gear differs depending upon which side of the output shaft the driven gear is. If the incorrectly angled gear is installed, the effect is to rotate the speedo cable backward. Generally, automatic transmissions have the cable entering from the driver side whereas four-speed units enter from the passenger side.
You will have to locate the correct parts from a good parts vendor as the local shops will have difficulty from their suppliers. Most vendors who specialize in engine/transmission conversions are quite familiar with this situation and will have the gears you need. Don't forget to obtain the correct driven gear, as the angle of the driven gears are also opposite each other and must correspond with the drive gear.