I concur, the 440/375 cam would work nicely. The closed chamber heads are fine, as the later orientations went more to mixture turbulence than the perceived better breaching of the open chamber heads. Adding the 1.74 exhaust valves to your existing heads, plus some bronze helicoil valve guides will put them close enough to 906s, I suspect. Why not start with some used 906s? With a main difference being the larger exhaust valves, IF you also want to put hard seats in the heads, pretty much the same place when you're done if you upgrade your existing heads. Plus, you'll have to pay for the 906s. Clean up the casting flash in your existing heads, port match the intake, and you're done. The ONE real, verifiable benefit of the 906s, with your engine, would be to lower the compression ratio so that normally-available fuels can be used without really needing the more expensive super unleaded fuels.
Of course, matching valve springs will be necessary. With the heads off, that's the best time to do it. As the lift of the cam is should be within the range of a stock HP cam for your model year, you might can delay this. Might do pretty well anyway, but the existing springs will need some checking, so might as well replace them as you'll have to remove the old ones anyway, to do the checks.
To me, ONE reason to use a stock-based cam is the lobe separation of about 114 degrees. This ensures a nice idle with plenty of manifold vacuum at idle. When I put in a cam with 110 degrees LSA, I had to redo the distributor advance curve just to get it to run as expected. Had to play with the idle speed/mixture to get it to idle decently in gear with the a/c on, too. NOT
plug-n-play as expected. Took a bit more to make it work, which was unexpected. Comp is a good brand that's been around for a good while, but some claim they don't use Chrysler-size lobes, but adapted Chevy-style lobes, if that matters (at least that's what Hughes Cams claim).
Aim for a 2.25 or 2.50" exhaust system, with some Street Hemi-spec mufflers. On the C-bodies, make that ;'72 Imperial mufflers (same C-body size case as the stock mufflers with the internal restriction of the smaller Street Hemi OEM mufflers), to which you'll need to match the 2.5" pipe size, inlet and outlet.
When doing the swap, do NOT scrimp on cam lobe, valve lifter lube coatings, lube on EVERY moving part, period! Top to bottom.
If you don't already have a roller timing chain, either the Mopar Performance item or the Cloyes Plus Roller are good choices. The Cloyes chain kit went well past 400K miles in one of my daily driver cars. BUT when I put it in, I used the cam pre-lube moly paste on the surface that contacts the engine block, poured the GM EOS (pint, at that time) over the sprockets and chain, too. Those items get lubes by "splash", so they needed some initial help, as the cam
lobes do.
Take your time, follow the FSM, especially when torqueing down the rocker shafts.
There are some people who have their own little tricks and such, which are things they've determined that worked for them. Nothing wrong with that and it is to be expected. Just arm yourself with the base knowledge of what the FSM had in it Proceed with that base knowledge and you can investigate the other knowledge as you might desire. It took me several weeks to get enough courage to do a cam/intake/carb swap on my '77 Camaro, but I did it. I did need more help in the final lifter adjustments, though. That was at 92K miles and it was still going good when we pulled it out and put a 350 in at about 550K miles. Had to replace all of the freeze plugs anyway, with the 350 having been built years earlier, as a planned upgrade that kept getting put off. BTAIM
Enjoy!
CBODY67
