I will try the 120 then. Thanks again.
The only paint “quality” I strive for is “doesn’t flake off.” 😂

You'll need to remove oil/grease, etc. before it's media blasted; otherwise, the media will stick to whatever is on the manifold. Paint & rust aren't a problem. If you take it to a machine shop to be media blasted, they'll probably put it in a parts washer or bake it before blasting it, but they might charge more than if you bring it to them clean. 

If media blasting is done properly, it will remove all greases, carbon, paint, rust and actually anneal the surface of the metal a bit.  That is why I do not recommend using glass beads for they imbed many particles instead of removing them.  Many machine shops use steel shot to clean parts and pressure wash them afterwards.  I don't like either steel shot or glass beads due to their getting caught in the tiniest of grooves or cracks in the part.  Steel shot will get into screw threads and ruin them.  Joe-JDC

JDC

HMMMM... Could I hit the suspect areas with brake cleaner or even a MAP gas torch (not necessarily in that order)?  I would think that would get rid of all the grease/oil.  Thoughts?

When my heads came back from the machine shop, I thought they were clean enough to paint; unfortunately, the paint didn't stick. I was able to remove the paint with Goof Off with very little effort. I then went over the heads multiple times with 91% isopropyl alcohol (cheap). Once my white rag was clean enough to suit me, I resprayed the heads, priming them first. Success!

Thanks for the tip...I had planned on using acetone but I do have a bunch of rubbing alcohol.  The blasting media is supposed to show up tomorrow, let's hope my old sandblaster gun still works.  It's been a long time.  

I used a cheap brass-wire brush for scrubbing, cheap paint brushes for applying the alcohol, and old, white T-shirts for wiping it off. I might have used 000 steel wool as well for the last step before painting. As long as you follow the directions on the can(s), you can spray the top of the manifold and then flip it over to spray the bottom (it's too heavy to hang). Seymour PBE primer dries very quickly; it's the best rattle-can primer I've used. The Seymour Ford/Chrysler Red top coat takes considerably longer to dry. 

I masked off all of the gasket surfaces before painting, but not everyone does.   

I plan to do the same with a manifold that I just picked up. I can have it sandblaster by a local company down the street.  Bit, how about the heat tube that runs through the manifold. I have heard they rust out. any experience on replacing this?

Are you retaining the original heat-riser choke? 

The heat riser tube replacement is a 10 minute job with the manifold off.  I used a small punch and carefully knock the old tube out and then use a small hammer to insert the new tube.  Once it is replaced, it should last another 30 years.