There are tricks of the trade that get put into the turnkey motors that don't get into the kits. Plus the options list is almost endless. Coated bearings, pistons, ARP everything, Jake even has some process that makes the crank and rods look like polished chrome. I guess it makes the oil slick right off???
The kit is the kit. Jake would have to know you and trust you to vary from the kit much. His name is stuck to the motor. You screw up, the shit still sort of lands on him.
The turnkey comes to you on a crate broken in a controlled setting on the dyno, the first oil change and valve adjustment done. You install and abuse.
The kit requires break-in in the car while driving public roads at the mercy of public traffic. Always a compromise. Then after a 1000 miles, you change the oil, adjust the valves and abuse...
The turnkey motor can cost as much as you can imagine...
The kit price is right there on the page. Not a penny more. It is so complete I sent Jake an email because I was sure that the six pack of beer was left out. Everything else was there though...
(I am not advocating intoxicated engine building. Engine building while intoxicated is illegal in 33 of the 50 States. Please don't drink and build engines
)