Before any work is done, measure the head for warp. Warped heads can be flattened, to a point, by bolting the head to a flat plate and heating it. Machine shops can do this.
The easiest way to remove and replace the guides is by using liquid CO2. The guides will drop out and then in.
Valves need to be faces on a valve grinder. Seats need to be ground in place, I'll post some pictures soon.
If a seat needs to be replaced, heat the head in an oven, not your kitchen oven but an old one that used to be in your kitchen.
1st pic, facing a valve.
2nd pic, con rod comparison, M180 rod, Porsche 944 rod, generic US V-8 rod, dragster rod
3rd pic, M180 block being bored for next piston oversize
4th pic, honing the cylinders.
I'll find some more pics. soon.
I hope this helps.