I will soon replace the inner wheel wells and front fenders on my 77, however; it will be several weeks/months before the truck is ready for a complete paint job.

Should I primer the parts before installing? What type/brand of primer? Your help and input is appreciated.

Unless you have a really compelling reason to replace them now, I would advise you to wait until you are ready for the bodywork and paint.

Otherwise, use a good urathane primer and that will do a good job of protecting the parts while you wait for the paintjob.

If you are going to drive it while it is primed....use an epoxy primer.

In fact, I epoxy prime everything now. The epoxy costs a little more, but it is more that worth it for the extra protection/adhesion IMO.