I would not use anything other than the recommended stuff on those crankcase faces, especially nothing with silicone in it. This sealing area is critical. Inappropriate sealers may dissolve when exposed to fuels/heat/exhaust. Too much sealer will ooze into passages and might actually shim the crankcase halves apart. Not enough sealer will create leaks that can only be repaired by disassembling the powerhead again.
Like I say, there are two options. The conventional OMC “type M”/847 sealer. The upside of this sealer is that it dries hard and won’t leak. The downside of this sealer is that it is messy to work with and dries quickly. So, assembly of the powerhead halves must occur quickly after the type M/847 is applied or the sealer will set up and the halves will be shimmed apart. The OMC “gel seal” is an anerobic sealer, it only dries in the absence of air. So, there is plenty of time to apply the sealer and bolt the halves together. The downside of the gel seal is that it won’t set up if the crankcase faces are oily/greasy, then you will have crankcase leaks when you start the engine. I would contact loc tite, I’m sure they make a comparable product to the OMC gel seal that is an anerobic sealer that is meant for this job. I can not over emphasize the importance of proper prep and sealing. Do it wrong/use the wrong stuff, and you have to pull the powerhead apart again to reseal.
I would not attempt to file the piston rings. Something is wrong if there is no ring end gap. I would give the cylinders a very light honing, remove the rings and measure again. Use the piston to square the rings up in the bore, measure the end gap in a few different areas.
