In my opinion model engine plans are guidelines. This is the reason model engine designers leave tolerances OFF the prints. In a shop environment today, any dimension is acceptable, like others say, it's the tolerance that kills you. Producing anything that must have interchangeable parts leaves you with little option. Just don't be surprised when quotes come back at a ridiculous price.
When I'm building a part for myself, I decide what will and won't do for dimensions and tolerances. When I'm designing a part for production, I must consider many requirements, production cost, how the assembly works together, the requirements of a particular component, etc. Usually there is some aspect of the design that constrains a dimension, and rarely is it what tools are int he machinist's tool box. If he doesn't have a 0.1330" reamer,
he can pick up a catalog to get what he needs. If cost is top priority certainly the availability of tooling should be considered.
I think that the ISO system for shafts and fits is a wonderful thing. You can buy shafts and reamers in the tolerance you need to make what you want to make without much effort. That is, if you work in metric.
If you don't like a dimension on a model print you're building, change it to suit your style. It's not a big deal. Part of being able to build a model engine is understanding how the parts fit together to do the job intended. The actual dimension usually isn't critical, just the fit.
Reamers for fractional sizes 1/8-1/2", .001" over/under sets are very common. I don't have a set, but I don't do much with shafts and reamers. But have purchased a few single pieces that were sized for the fit I needed on the shaft.
Greg