Not being familiar with the Colorado parts, do the manual transmissions use a separate bellhousing or is the bellhousing a non-removable portion of the the tranny? If removable it should work with the 6. If not you can always make an adapter plate, like hooking a TH350 to a 235, to connect a conventional pattern bellhousing. You will probably want to space the flywheel out a similar amount. You will definitely need to rebalance everything when you add the clutch etc to the motor.
Also, not sure on the crankshaft, but make sure you can find a flywheel that will mount up and support a clutch that will handle the power this thing will put out.
I definitely understand your wanting to use a manual trans, but in this case an automatic would make things considerably easier.
