It is quite feasible to build a 38-55 on a #1 rolling block, that is one of the most suitable cartridges for it. It will make an excellent rifle, if used with black powder or reasonable smokeless loads.
The condition of your project should be a concern though. Parts for the rolling blocks are neither plentiful or cheap. I have probably more parts for the rolling block than almost anybody in the U.S. (not offering to sell, though) and I can tell you first hand that it will be tough to find an appropriate breech block for your action. Hammers and other parts are relatively easy to come by, but I probably get 5 or 10 loose hammers for every breechblock I get. When I get a loose breechblock, it often is a non-standard size or in poor condition, left over from someone elses earlier mistake. A good breechblock will usually bring around $100 on the parts market.
There are castings available from a couple of sources, but unless you are very good at working on rolling blocks I wouldn't even consider doing that. The rolling block is a deceptively simple action with few parts and what looks like non-critical dimensions. But, the relationship between the parts is critical to work correctly. That's why all the rolling blocks are the same. Once Remington worked out the geometry, everybody else copied them, because that's what works, and it's hard to arrive at different geometry that will work. Some of the swedish RB's are different, but they don't differ by a whole lot, usually only block width and extractor style.
Bottom line is that if you want this to happen, find a complete, workable action and start from there. Starting from parts and assembling unrelated parts into an action is not an easy path for your first RB, and will probably run more money before you're done.
Best of luck,
dave
