On on engine like this, there only needs to be 50% contact area on the Taper between the Crank and the Flywheel.
Looking at the Crank as is, I'd say cleaned up, you'd have close to 70%, but clean it up first.
this is a promising sign. I'll take the crank out and check with my local machine shop if he can weld and resurface it to fit a new flywheel boss. If the cost is similar to changing the crank then i'll just change the crank.
sigh... feels like all the effort from the past 2 months rebuilding the engine has been wasted...
Cleaning that crankshaft taper will take a lot of meat off, then the interference fit in the flywheel boss will be lost. This part of the crank takes a fair amount of torque and weld building up is fine on journals but I would be hesitant to do that on the taper.
If it was me I would get another crankshaft, 998s are common enough.
In cleaning it up, I'm not suggesting 'machining' it back at all, only taking off the high spots on what's there now.
While I did suggest doing it in a lathe, if you take your time, you could do it it in the bench. Starting with a 2nd cut file, taking probably only 4 or 5 strokes at the most to take off the highest spots, the finishing with a Diamond Lap from there. It will take a bit of time,but the diamond lap will really only take off the high spots.
Of course, if a replacement crank is easy and cheap enough, they would be the best and easiest option, however, I know with where you are what a 'struggle' it's been up to this point (financially), a repair might be the best option?
Regardless of how the repair is done, key to keeping these tapers in good order and workable is getting the flywheel on really tight. The damage you've done there is mostly from the flywheel fretting (basically rubbing) on the Taper of the Crank and for some time. That's what damages them.
When I fit these together, after a light lapping of them together, I lube up the taper with a very very like smear of 3 in 1 oil, then really heave down on the Flywheel Bolt, probably getting to 150 - 180 ft / lb. Under the extreme pressure exerted on the taper, the oil film breaks down and there's a good friction joint between the two parts - and no fretting ! You will need a good flywheel puller to get them apart, but you can be sure that the taper on both parts will be in perfect condition.