If you want to install the fentons, or do a home made split manifold out of what you have, go to it! It’s a fun project. Tubes from the exhaust to the bottom of the intake, take a pass, they don’t work all that well. Run hot water to the bottom of the intake. Langdon has a plate that might fit a stock intake, otherwise just make one up with two fittings for inlet and outlet hot water. Tom has some other parts to help with this, a spacer for in between the therm housing and the head with a fitting for hot water, or you can use a 50s era gmc lower therm housing. Some come with a port on the driver side already drilled and tapped, others, just the boss so you drill and tap for the hot water.
Using the stock manifold, as mentioned above, has some great benefits. Primarily the use of the stock heat riser. So you split the manifold, weld on a cap one each end, install an outlet on the part that has no outlet, and you have true split manifold with factory heat riser.
Fenton use to make a split manifold with a heat riser but they are pretty rare.
You can also simply add a second outlet onto the stock manifold and get dual exhaust and same deal, you get to keep the stock heat riser.
Clifford performance also makes a set of true tube headers. Want to hear how they sound on a 235 chevy:https://youtu.be/jYeeUfxGwlY
You can put a set of electric cutouts on those headers and open them up if you felt in the mood.
I have run headers on all of my 235 and 261 motors for over 40 years. Go ahead, have some fun!