I bought my %.3 and 6l80e from Tilden motorsports in Gilroy ,Ca. They were very easy to deal with and patient as I wanted an engine without DOD and it took a few months for a clean low mileage one to turn up. I thought their prices were good and they do test run them and send you a short video before you purchase itWhere is a good place to source out these motors and trannys? Car-part.com?
I have been studying the new LT1 Gen5 setups. There is finally some recent info coming out about them. Since they will take an entirely different exhaust manifold, new block hugger versions will probably be necessary. No power steering pump so that will have to be addressed. There is a vacuum pump where the power steering pump would reside. Supplement vacuum is necessary for the brakes as there isn't sufficient vacuum apparently. Holley does make accessory drive brackets and show the power steering pump in the drivers side and state the vacuum pump can stay.
I am very interested in doing this swap. My company truck is a 2015 Silverado 5.3 and is so smooth and powerful. I want that in my LX450 as well but may opt for a gen 4 and 6L80.