Back to the original intent of this thread.
You mention your 3-53 engine has an SAE #4 housing. Depending on what transmission you choose you might have more luck with a SAE #3 housing on the engine.
Original 53 series flywheels that fit automotive type clutches are sometimes hard to find and when you do they are usually SAE #2 or #3 size (possibly always, not sure).
It may be possible to modify one of the hundreds of different other 53 series flywheels to fit a clutch suitable for your new application, but it's generally easier to do conversions with ready made parts and avoid machine work when possible.
Before getting to far into wrenching on your conversion start trying to plan dozens of steps ahead in an effort to sort out as many of the big issues before they're actually issues.
By changing to a #3 bellhousing I could use all stock GM parts, but with the cost of those parts these days it would cost me a fortune.
Phoenix Machine makes an adapter set for the #4 bellhousing and #10 flywheel (which I have). It's only $480 for the set. The advantage of using the Phoenix adapters is that I can use my existing bellhousing and clutch linkage. It moves the engine 3/4" forward, no problem as I have lots of room with the 3 cylinder. The only downside I can see is that you end up with two flywheels, and their weight (in my opinion) will make the engine want to keep spinning and not run down between shifts. The folks at Phoenix say it hasn't really been a problem.
There are a bunch of other outfits making basically the same adapters, but selling them as Kubota to Chevy conversions. Kubota also uses the #4 bellhousing and #10 flywheel. The difference is they are asking a bunch more money for theirs. ($1600 but they include motor mounts).
