Here's some info:
The Novak Guide to the
Borg-Warner T18 & T19 Transmissions
The T18 or T-18 Transmission The T18 is a reknown, heavy-duty truck transmission designed for and used in ½, 3/4 and 1+ ton trucks. The T18 was made by Borg-Warner Gear from 1966 to 1990. They are found in Ford, Jeep and IH trucks. The T18 is the improved successor to the T98.
Features
The T18 is a top loaded, top shifting truck style transmission. The Ford and some Jeep T18s enjoys a very low compound gear at 6.32:1 and as such it is a popular choice for those wanting a very low crawling gear. T19 versions offer a 6.32:1 (IH), 5:1 or 4:1 (Ford) low gear.
The T18 is fully synchronized in the second through fourth gears. All gears are helically cut except first and reverse, which are spur gears. T19s are syncrhonized in all gears and feature all helically cut gears.
http://www.novak-adapt.com/knowledge/t18_t19.htm
The Novak Guide to the
New Process 435 Transmission
The NP435 Transmission The 435 is an excellent, heavy-duty truck transmission designed and used in ½, 3/4 and 1+ ton trucks. It is a well-built transmission and remains easy to locate and generally inexpensive to buy and maintain. The strength, relatively short size and the gearing of the transmission make it a good choice for a variety of situations.
The NP435 was made by New Process Gear from 1964 to 1993. They are found primarily in Ford trucks from 1966 to 1992 and Dodge trucks from 1964 to 1993. They also had limited distribution in GM & Chevrolet trucks from 1968-1972.
http://www.novak-adapt.com/knowledge/np435.htm