I might as well add my tuppence worth. I'd say if you timing bush is shot, then for the time and cost involved, I'd recommend upgrading to the needle/ball end-feed for the timing side.
I agree with Nick that it has to be machined correctly, but when done it all fits together straight off every time. And as you pointed out the Brg run's on the inner race and NOT on the actual crankshaft, plus, once fitted unlikely to wear out in your lifetime.
Pre 67 engines do require a little weld on the crankcase to bring the oil-way transfer to the inner timing case if going for the integral system. Again I'll agree with Nick in that its not a good idea to weld on the timing cover due to the potential chances of distortion, however its easy to make a seal carrier block which can be bolted or held in place with modern metal adhesives, the plus side in end-feeding the crank is that you have gained at least an extra 25% oil supply to the big-ends which wasn't available with the bush. So your old oil pump is good to go, I'm assuming it's been rebuilt correctly.
As for the EI, well I'll leave that to better qualified people to comment on. But I think it'll be something else that will break or fall off when you're out on your "Old Crate" that will stop you getting home. Sorry Nick couldn't resist steeling your description.
In advance, sorry if I've hurt anyones feelings.