Some folks advocate blending.
There are; however, problems inherent in doing so. The two liquids, #2 diesel and VO may well seperate into layers and you could end up burning unheated straight VO. That can result in coking which can lead to engine failure, it can also lead to fuel pump failure.
If you want to run VO the two best methods are convert it to BD and use it like #2 or convert your truck to straight VO, this involves two fuel tanks and a heater for the VO.

Your 86 IDI engine will do well on VO, if you do it right.