The ports that need the most reshaping are the exhaust ports. Exhaust gasses right out of the chamber are way hotter than any of those liquid aluminum or JBweld products can handle. Like 1200 F ?? I would be skeptical of that working for very long. I found a local welder that does a lot of prototype injection mold tooling work. He welded my exhaust ports adding abouta 3/4" in the area I specified. He charged me $100 for both heads. When he did that, all my valve seats fell out. So after I reshaped the ports to how I wanted them to look, I had to get new valve seats put in. If your gonna reshape the ports, you'd prolly want new seats anyway so you can run bigger valves. It turned out that my heads were not as warped as one might think from all the welding heat and they straightened out with about .010" of resurface.
To figure out how to reshape the ports, modeling clay works great on a flow bench.