Standards are good things to have... they keep you on the right path. Depending on the "standard" or path you've chosen you can have an easy time or a very difficult time. Fender Guitars due to the length of their production runs and the shear number of guitars made represent the easiest path for the first time Fronkensteener. Although they can sometimes lack the sex appeal of a more rare or obscure guitar; starting off on a learning path with a smaller curve is wise.
One thing you should be absolutely clear on - from guitar maker to guitar maker everything changes - a perfect example is the two neck plates ABOVE - the black on on the left is a generic plate from a Jackson/Charvel electric guitar. It uses the Fender neck bolt pattern and is compatible with Fender necks and bodies. But this DOES NOT mean that Jackson/Charvel necks will fit or work with Fender bodies... they won't.
Then neck plate on the right is a standard Kramer Guitar neck plate - it WILL NOT fit Fender necks or bodies for the bolt pattern is smaller - which is ironic because many Kramer necks WILL fit Fender Stratocaster bodies - but because the neck bolt holes are all wrong you have to use wood filler to "fill in" the old bolt holes and then drill new ones. This is tricky because the old holes are close enough that the new ones will mostly be in the wood filler - and so if this whole process isn't done correctly you'll have a neck that is not as stable as it should be.
Which brings me to the FIRST LAW OF FRONKENSTEENING - Do NOT ever - and I mean it - EVER - modify or alter a true vintage piece of gear because in doing so you will destroy its value and trust me you'll kick yourself later. Many vintage guitars are worth tens of thousands of dollars now if they are completely original and unaltered. Condition isn't near as much a factor as originality. Old guitars are like old pieces of furniture - refinish them and you destroy their value - change the rusty screws out to new shiny ones and you destroy their value.
The issue with FENDER STANDARDS - (ABOVE) - so you quickly learned in the first section of this card that neck bolt patterns between guitar makers are rarely compatible - the sad thing about Fender is that there are dozens of changes to neck bolt patterns through the years that make many Fender necks incompatible with each other. Forget the Kramer neck plate above - the other 4 plates are all Fender plates and NONE of the necks that go with these plates will work with bodies from the others. The bottom two plates - the differences are pretty obvious. The one on the left is a "contoured heel Stratocaster plate" - the left is a 3-bolt (1970's Telecaster/Stratocaster plate). The first two plates on the top row are identical - one being a newer Jackson/Charvel plate the one in the center being a vintage Telecaster plate - the issue with necks from a Telecaster and Stratocaster is simple - the heel of the neck where the neck rests into the body - these shapes are different on these two guitars. Think of guitar necks and bodies as "puzzle pieces" - you want them to fit each other perfectly. There are many reasons for wanting a tight neck joint - the most important being stability - the more stable the neck the less issues you'll have with the guitar going out of tune. Guitar strings place enormous pressure on the neck and neck joint of a bolt-on guitar. For this reason it's never wise to build a guitar with a neck that doesn't fit perfectly into the body's neck joint.
So - you have a few things to work out in your guitar build BEFORE you even get started. Call it homework or research - it's the stuff you have to get straight before you start buying parts (and thus potentially wasting money and time). ABOVE - Even though Fender neck pockets are pretty much always going to be 2-3/16" or 55.56mm - you can't just take a Fender neck and slap it on any Fender body. Many necks (by makers other than Fender) are too wide or do not have the proper heel shape.
The first reason is a matter of physics - the two neck joints may be the same width - but the neck won't seat into the joint correctly because of the shape. A rounded Stratocaster neck WILL seat into a Telecaster body and be playable. It will have some gaps where the neck and body do not connect and this can be problematic for overall neck stability. A Telecaster neck WILL NOT seat correctly into a Stratocaster body; the reason for this is the SCALE LENGTH of the guitar.
The DISTANCE between where the strings leave the BRIDGE from the BRIDGE SADDLES to where they connect with the HEADSTOCK (AKA peghead) of the guitar at the NUT - this is the SCALE LENGTH. The overall scale length will determine the placement of the frets. Move the frets just a fraction and the entire guitar will not play in tune. I'll go into scale length in greater detail in a later card.
BELOW - Two necks with IDENTICAL neck heel shapes - both will fit a Stratocaster body - but only ONE neck will actually work and tune correctly.
IN REVIEW - Make sure that you know what standard you plan on using when building your guitar and know that just because there are all sorts of options out there that may fit - they won't necessarily work. There's a lot more to building guitars than meets the eye - there's a lot of math involved - and not just math but fractional math!