Good onya Razor. is it the light metallic blue one from ozdat?
They've got the L24 six cylinder, so the L26 and L28 motors bolt in. Like the A series, the numbers represent capacity. Heads and internal parts are interchangeable too, and there are some heads that are better for performance than others, but I don't know the codes off the top of my head.
Front struts are interchangeable with
most other Datsun struts, and the coupe should have the twin spot front brakes that are commonly used as an upgrade for lighter 4cyl Datsuns. They're not great on the heavier 240K, and probably the best value upgrade is the popular Verada blank disc/Commodore caliper. But you can also use the later (larger) 240K disc on the standard hub with a 260Z twin spot caliper, but it's not a great improvement.
There is a bolt in rear disc upgrade from the MR30 Skyline.
Try the Classic Z forums, there are a few C110 Skyline (sounds much better than 240K) owners there and even the Z owners have some appreciation for them. Just remember that it is a Z car forum.
http://www.classiczcars.comand Ozdat has a couple of K owners too.