I've used Painless on 2 cars that I built for other owners. The kits worked out very well, mostly because they wanted additional circuits to run accessories the factory didn't use (A/C, C/D players and amps, etc).
The kits I used have only a small 1 1/8" or 1 1/4" hole that has a grommet seal around the wires. I took out the factory plugs and welded/sealed the square holes with 16 ga sheet metal, then used a hole saw in the same exact spot to make the round grommet hole.
It really depends on how many things you might add to your ride as to how many circuits you should have. I'm a big fan of lots of cicuits, and the Painless fuseblocks are nicely marked as to which fuse takes care of what. If you go with an original type and then retrofit more gadgets, then it's up to you to remember what wires you tied into in order to get the power out.
Hope this helps.
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David
