A Briggs dealer would be able to suggest a replacement if you give him the model and type number. You might need to shim the new engine so that the crank alignment remains the same.

Check out www.northerntool.com
I replaced an 8HP Briggs on my wood splitter with a new Briggs OHV engine and it really worked out well. I had to raise the engine mounting plate approximately one inch to make it physically fit but other than that no modifications were necessary. The dimensions for each engine are listed on their
web site and they were about $20 cheaper than anyone else. I had the engine 5 days after ordering it.

Email Small Engine Warehouse with your numbers and they will tell you what will work.