Tim,
The reason the Club doesn't stock front main bearing bushes is that most engines either have undersize crankshafts or oversize bearing housings in the crankcases, or both, so bushes usually have to be custom made.
Firstly, I would make the front main bearing bush the same overall length as the front journal on the crankshaft - this will mean that it will project into the timing chest by the same amount as the thickness of the flange on the front half of the old 2 piece bush. Also, your crankshaft should have an oil groove around the front journal, so there is no point in machining another one in the bush. The early one piece bush just had a single hole to line up with the oil gallery in the front crankcase half - it is important to get that positioned correctly relative to the cutout in the flange that fits over the locating pin. 1½ to 2 thou interference should be fine on the bush, but DON'T use Loctite - it does not discriminate - it will just as easily lock the crankshaft into the bush as the bush into the crankcase. Camshaft bushes only need 1 to 1½ thou interference, but don't make the bores too tight - they are only splash fed, so the oil needs enough clearance to get into the bush and do it's work - something as trivial as a tight camshaft bush can make a motor noticeably sluggish!
Regards,
Eddie.