TR4A project

[Perdido]

Howdy!  I'm starting a project and I have lots of bits and pieces and need/want everyone's input.  The car body will basically be stock, but I want to put a more modern drivetrain under it along with suspension and brake upgrades.  I have a TR6 and a TR4A frame, both have been upgraded/reinforced and the 6 is painted, the 4A is powder coated.  I imagine that the 6 frame will be the best starting point since I would like to use a more modern straight 6 in the 250 hp range.  Options appear to be BMW, Toyota, and Nissan and I would use the same brand of transmission and possibly the diff.  I prefer NA over turbo, but I won't rule a turbo out which leads me down the Ford and GM rabbit hole...something like a Mustang drivetrain.  The bits and pieces that I mentioned are in the form of 3 TR4As, a TR4, and 2 TR6s.  One TR6, one 4A and the 4 I consider to be restorable, but in reality parts cars.  I've got a decent shop with air, a lift, and welder plus hand tools and some fab equipment and more time than skill.  What have y'all built that fits my basic outline?  This will my first foray into a project like this and all my former projects are relatively stock...an MGB, a Bugeye Sprite, and a 66 TR4A.
Thanks, Rut