I have a few of the long tube scopes. One is a Lyman full length tube that is on my Ruger #1 Lyman Centennial .45-70. The other is a old Tasco brass tube replica, which is on my Hepburn, also in .45-70.
These scopes work well out to 200 yds max, with the external adj. mounts on them. The limit of these scopes is the low magnification, and lack of elevation in the mounts to shoot really long range. 
The original Malcolm scope mounts had a bit more elevation, so they would reach out farther, before running out of elevation. 
I put a set of Winchester mounts on the Tasco, because the factory mounts were so poor. The Lyman has their own mounts, which are good, but neither are click adjustable. They work good at the 100 yd. range, and I hunted elk with the Ruger a couple years ago, and it worked very nicely.
I think a company called Leatherwood has just come out with a new repro Malcolm type scope, and there are several others making decent copies also.