The alternator that replaces the generator is expensive,and less reliable than the Lucas type alternator.I don't think it even produces as much power as you can get from a Lucas alternator;you can get 180W @ 5000 rpm thesedays,single-phase or 3-phase.
You can still use a Lucas alternator with generator cases,you just need the alternator primary cases.You just need to plug up the generator hole in the crankcase,if it's not being used.
T100 and T110 got big bearings in '54 model.5T and 6T got the big bearings in '55.T110 used generator and magneto until about '59.5t and 6T used alternator and distibutor,since about '54.
A light crank might be fun when you first accelerate in the low gears.It will make more vibration and less power.The crank used by Johnny Allen at Bonneville weighed 10 lbs more than standard.If you use a unit crank,you need to trim some thread at the timing side,so it doesn't interfere with the bush in the timing case (or shorten the bush).
Use a clamping washer between the timing side bearing and crank pinion.There's a narrower pinion gear for this.That allows you to use a roller bearing on the drive side.Check that the conrods are central in the cylinders,and shim the crank if necessary for rod alignment and end-float.
The lightest flywheels were '66-'68,and even some in '69.Rods got heavier and stronger during '67,and more crank counterweight was used to keep 85% balance factor.You only want about 71% for a pre-unit.Rod bolts changed to UNF after June '69,and these only get torqued to 22 ft-lbs dry (or still 0.004"-0.005" elastic stretch).
Cranks made after mid-'71 have a bigger metric bearing on the timing side (30 mm vs 1-1/8").You can grind down a metric bearing to fit the pre-unit big-bearing case (about 0.020" to grind off the O.D.).They also used UNF flywheel bolts,instead of 3/8" x 26 BSC.That means it's easy to find better grade-8 bolts.
Cranks '73 and later have a longer alternator snout to clear a triplex chain.You would need to shorten the snout to clear the primary case;not difficult.