Rather than making a new guide from scratch, assuming the valve stem to guide clearance is about .0015-.0020, it might be a good idea to look into the idea of plating up the outside of the guide to increase its size.
Ideally a nickle or chrome plate would be used but if the guide is only a couple thousandths smaller than what it needs to be, a simple copper plating would work.
Copper plating is relatively low cost and it shouldn't require machining the outside of the guide undersize prior to plating. Just a thin coating of a couple of thousandths (.002-.003?) thickness of copper per surface is all that is required.
(Nickle or chrome plating needs a copper undercoat and the combined thickness of the undercoat plus the top coat can amount to several thousandths per surface. For that reason, often the basic part needs to be machined further undersize before the plating can be done.)
Getting the guide copper plated isn't a job for the shadetree mechanic but almost anyplace that does plating will have the ability to do copper plating.
The only thing to remember about using copper plating is, it is a soft material so it won't like being pressed into the cylinder head if the head is at room temperature.
Heating the cylinder head to 300-350 degrees F (149-177 degrees C) in an oven and chilling the guild in a refrigerator ice box will greatly reduce the interference so just a light tapping with a mallet should seat the guide fairly easily while leaving enough copper plating to maintain the press fit.