I'm working on a similar swap too.
I'm putting either a '75 or a '76 Cad 500 with TH 400 into a '54 or '55 1st GMC 1-ton. If you are using a rear drive motor you need to know it has a front sump pan, and you'll need either a rear sump Eldorado pan or a mid sump pan from a later 425.
There are some differences between your Chevy 3100 and my GMC 250, but most of the issues will be the same.
I did not see a way to clear the toe board and keep the bell housing crossmember in place. My decision was to remove that crossmember allowing mounting the motor lower and a little further back.
That does make the interference between the exhaust manifolds and the frame a little too tight. I've not solved the problem yet, and may end up trimming a quarter inch off the inner edige of the frame rails.
There is no way to retain the stock steering.
On my GMC I see the oil filter interfering with the engine crossmember. Choices here are a remote filter or cut that crossmember out of the way. I suspect you will have the same problem.
Those are my initial thoughts. I'm also converting to IFS on the front of mine, in part because I removed the crossmember between the spring mounts, and in part because I wanted to get modern brakes.
I see no need to relocate the master cylinder but would suggest adding that much power you really want to augment your brakes too!
Today mine is stripped to the frame with the IFS install underway. I don't expect to finish that for some time, and won't remount the cab or test fit the motor again for months. But I want to hear how your project is going and will be happy to answer any questions about my project that you can ask.
