when multiple manual transmissions are offered in one truck, are they interchangeable? I have an orphan T170RTS in my 1984 F150 that needs repair, is hard to find and apparently not suited for heavy duty. the same year truch also used NP435 and T18. also, newer trucks use a ZF5. how can I find out what is easily interchangeable? I not swapping in a V8 but we are boosting the power on the I6.