I'm not acquainted with your 612, but if it has a hot shoe or other strobe mount, there are lots of spirit levels around that qualify. I can provide a link for that style if needed. Without the mount, I'm not sure which style of level will work.
As for lazer rangefinders, this model
is representative of what might suit you best, both in terms of features and lowest price. Beware of versions that brag about great distance capabilities to 800 or 1200 yards for general use at closer ranges. Models with lower ranges such as this 400 yard model are generally more accurate inside 100 yards. The +/- $200 price point is about as low as you can go while getting the durability and reliability to make the investment worthwhile. There are lots of other models on the linked site and others, so you can do your own comparison of features and prices.