Hi Dazz,
One needs to be careful laying a level across the bed of the lathe if it has triangular ways like the Boxford A,B or C etc (Southbend 5?) as the tops of the wayts at those points are not machined just lightly dressed as they are not bearing surfaces it is not worth the expense of accurate machining. That means that there may be a slight diffence in relative heights which could make the laser inaccurate using two different points on the ways. In this situation you need to use accurate pair of parallels on the flat portions of the ways to raise your level clear.
Twist is best checked and adjusted by turning a longish bar (say 25mm dia x 250 mm out from the chuck) without tailstock support. Just take a light cut along the bar and measure at two extreme points this will indicate any twist as the extreme outer end will be larger or smaller if twist is present, if perfect, thank your lucky stars and have a large glass of whatever you like to celebrate!
If the outer end is larger the bed is twisted towards you at the tailstock so the tailstock foot needs shimming at the front, if the taper is smaller away from the chuck then the bed is twisted away from you the shim needs to be at the rear of the tailstock foot. then retest and repeat until you get an acceptable reading, it doesn't take long. I should say that with my lathe I use a simple scissor (car) jack between czbinet and bed to raise the tailstock end by a few thou (US - mil?) to make it easy to slip the shims under as required.
TerryD