DON'T! Ebay has become famous with shops buying chinese knock off clutch packs and passing them off as top shelf. Also avoid Monster transmission in Brookesville Florida like the plague. As far as a good builder, it would really help to know where you're located. There's some really good builder's, and some REALLY BAD one's. Before you get yours built, do a google search of the shop, check online reviews, better business bureau, and facebook. Read the negative's and see if it's ridiculous stuff, or valid complaints. And don't be afraid to ask around locally at parts stores and such. And keep in mind a warranty is only as good as the shop doing the work, it's better to get a so so warranty from a top level builder than a to good to be true warranty from a crap builder. Places like Jasper have really good warranty's, but that's about all they have going for them.