If you go from a 5 bolt to a six bolt bellhousing you will have to change the transmission bolt pattern on the bellhousing to match the narrow pattern bolt pattern on the older transmission. The front bearing retainer for the top loader has to be replaced with the larger bearing retainer used on the later trans to fit the hole on the 6 bolt bell housing. Also, you need to get the clutch slave bracket for the six bolt bellhousing. The 5 bolt bracket used for the 5 bolt will not work. You should be able to swap the front timing cover from engine to engine. You need the old one for the dip stick location. I don’t think you need anything else.
Although cooling may be a issue if you use the original radiator. You may have to upgrade to a larger radiator.