Mill engines were intended for driving factory machines, and as such were very rarely if ever fitted with reverse. (If I say never someone will come up with an example.)
OK, a faceplate is a flat plate with some slots in it that screws or mounts onto the spindle of the lathe. It is a way of holding jobs that are too big or are the wrong shape to easily fit into a chuck. Since it is flat, it does need one side of the job to be at least moderately flat, and it can be a challenge to find ways of clamping the job to it so that the screws don’t get in the way.
if you don’t have one, it is something to consider possibly making or buying at some point. Making one can be a bit tricky since ideally you would want to attach the blank to the faceplate to turn it, and since the reason you were making one is because you didn’t have one….
in some of the smaller lathes, you will get a drive plate, eg the Unimat provides a little aluminium plate that screws on the mandrel and has three slots in it. This is intended as a way to drive a drive dog, which is used when turning between centres. It can be uss a faceplate for light work, but that lathe actually has a much better cast iron T-slotted faceplate available as well.
Anyway, so long as the hole you have made is reasonably true to the rest of the casting, all should be well. So next step is to turn a mandrel to fit the hole on a piece of bar held firmly in the chuck, with a thread on the end (which can be cut with a die) and mount the flywheel on that. You will only be able to take quite light cuts, since it may try to turn on the mandrel. You can use loctite to help too. If you made your mandrel out of a fairly large diameter piece of bar, you could consider tapping it near the edge for a screw that would engage with one of the spokes to provide a positive drive. The Stuart cast iron is generally excellent, but it is not unknown with any cast iron to find hard patches on the surface. They will usually not be deep, so if you are having trouble, you can consider a little careful grinding to take the skin off the offending patch. Carbide tools are of course good for this job, if you have them.
I should stop thinking of possible problems that p[roably won’t happen and let you get on with it.
regards
John