I replace alot of MG ring gears, and here's what I do, I got a big vice that that I can put the flywheel in, then I use a big hammer and a round piece of steel stock, about 1/2" in diameter, I just drive the old ring gear off, they are not terribly hard to get off this way, and you don't have cut or heat anything. Whe go back to put the new ring gear on, I get a couple of sets vice grip to use as handles and attach them on the other edges where they will not interfere with installment, I then heat the the new ring gear with a torch until I get it to the point it falls on the flywheel, they cool down quickly so work quick, I done maybe 20 or so ring gears like this and saw many more over the years installed this way at machines shops, if you have torch it's fairly easy job to do.
As for the aluminum flywheel deal, I ran them for decades on both street and race cars, I see no issue with them on street cars, I never gotten any of the idle issues you hear some speak of or noticed them be terribly hard to get off the line with, and know people who have been running the same aluminum flywheel for a 20 year stretch on both street and race applications. FWIW, I putting a new Fidanza aluminum flywheel on my new persoanl MGB engine, if I thought for skinny minute it would be a issue, I wouldn't do it.