Most modification mistakes are not workmanship mistakes. They are arithmetic mistakes made at the ordering stage: a tire two sizes too optimistic for the gears, a wheel whose offset spends clearance the truck does not have, a carburetor sized by folklore, a camshaft chosen without asking what it does to the compression the engine actually runs on. The fixes are all knowable in advance, because the relationships are published, stable, and computable on the back of an envelope.
That is what this library is for. Each guide takes one subject from the Digital Toolbox and goes the full depth: the definitions, the formulas with their constants explained rather than asserted, worked examples carried through to real part numbers and real gear sets, the failure modes in both directions, and the questions readers actually ask. Where a guide makes a claim with a number in it, the number is worked in the text where you can check it. Read the guide, then run your own combination in the matching calculator; the two are built to be used together.
New guides are added as the toolbox grows. If a subject you are wrestling with is not covered yet, the calculators in the Digital Toolbox each carry a plain-language explanation of the formula or data they run on, and the contact page is open for requests. Fitment questions with real consequences, gearing, compression, fuel system sizing, are exactly the mail we like to get.