If you already have the engine out, it's not that difficult to change the timing plate. If you set both engines with the front up on the clutch housing and have at it it doesn't take as long as you think. Just make sure you line the lifters up in the order they came out of the 270 because they want to be on the same cam lobe they wore in on. I think the time frame mentioned earlier includes removal and installation of the engine. The 6 bolt 6 volt flywheel is a scarce item. The asking price for them is usually close to $300. However, I did see one sell eBay last week for $100. If you are planning on switching to 12 volt, your 58 flywheel will work fine.