Small scale scratchbuilding help

[chrisaec]

Hi all,
I'm pondering the idea of turning an Armourfast 1/72 M10 into an M35 Prime Mover
Therefore, I've been thinking about how I could build a hull interior... But I have absolutely no idea how to go about scratchbuilding the parts like the transmission, especially in small scale

Any advice would be greatly appreciated
Thanks in advance, Chris