Trunion to u-joint conversion

I am building a new project, Petty blue 73 Twister 340, which was a 318 3-spd. I have an early 4-speed trunion type trans and was wondering what I can do to convert it to a u-joint type. Will the spline shaft from the three spd. replace the trunion? If not what do I need to do to convert it? Any help wold be appreciated.