I'm just about to fit the HS to the fuse and I could do with a digi level that will fit that section of the fuse. The opening is between 5" and 12", which model/make have you used?
There is a company that makes the Smart Level. It has a module that is maybe 8" long and it can fit into a 48" frame for use as a bigger level. Thats what I use.
The Smart Level is one of the best digital levels on the market as it reads in 1/10 degree. Some of the larger digitals only measure 1/2 degree. When I was measuring my horizontal and wings I would get them close with a digital level and then dial it in with a machinist bubble level. Way more accurate than even the Smart Level. Don