You always should lap valves in when you change them, you can't guarntee the seat in the head has worn in the same way as the valve you are about to fit, and for what time it takes i would always do it, just for peace of mind.

As for the head/head gasket, HOW MESSY is that head to start with its covered in corrosion, the mating face isnt even clean. I also bet the bolt holes are full of oil and crud, which then means when its torqued you will get hydrauliuc lock and its not actually torqued down accurately. When doing things on engines generally everything needs to be as clean as possible!

You may well of got away with re-using the gasket if it hasnt got hot, i personally though wouldn't recommend it all, its just not worth it.

I did wonder whether you would take offence to what i said but i felt i needed to say it simply because you are going to end up costing yourself more money.

If you were close by i'd happily pass through and give you a hand.

Just as an example when i took the head off my car, i spent a fair time cleaning the block face and the bolt holes etc, before refitting the head which was also skimmed, and to be honest i wanted to get it cleaner than that but it was getting dark