I don't believe the question has been answered yet...
We need more info about the 235 engine, is it early or late?
Pictures of the "new" engine and how the 261 sits in there already would be helpful.

Sure, they both fit, but there may be some different details to making each fit "just right". Without knowing what you have exactly we can't advise on those details.

Grigg

•1951 GMC 250 in the Project Journals
•1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
•1952 Chevrolet 3800 pickup
---All pictures---
"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-