Doesn't matter about manual or auto. If it was manufactured by Chevy for a Chevy between 1957 and 1998 then it will fit. If manufactured bt 1957 and 1991 then it will work with no wiring needed. V8, V6, or inline 6. inline 4 will need special bellhousing for manual. There are some diff ones - powerglide, turboglide, TH200, TH350, TH375, TH400 etc but only minor routing of cooling lines, vacuum modulators and shift linkage would be required. If neither of his 30 year old trucks has been modified then the 68 is a direct replacement for the 67.