Use care when OVER cleaning a well worn engine. Often times more harm than good is done. Removing all deposits and "crud" isn't always the best remedy if those deposits are filling in worn areas around bearings and/or seals.
The only time it's a good idea to clean an older enging "like new" is when you plan on rebuilding that engine to "like new" condition.

"expensive engineered sludge" LOL, That's great, I'll have to remember that one!

I wouldn't worry about changing over to synthetic at all.
Just clean and degrease the engine so you can detect any leaks you may already have and take care of those via proper torque or new gasket(s) as may be needed.

Don't think I'd add anything else to the crankcase, the synthetic will clean it up nicely after a couple of oil changes, just drain it after a drive and when it's warmed up so any suspended dirt/ particles flush out with the oil.

I've run Mobile1 10W30 in my 84 for many years and it's super clean under the valve cover. No need to change it too often, I do mine from 6000-8000 miles and that's probably too soon unless you live in a real dusty area or pull a trailer of drive it real hard.

I do a throttle body and air chamber cleaning every few years then use Seafoam to keep the top end clean. Run some injector cleaner through the fuel when you are down to about an 1/8th of a tank so it's concentrated then add quality gas after running the injector cleaner for 50 miles or so.

DLW,

I have a 1996 camry LE V6. used conventional oil till 150,000 miles then switched to synthetic oil. it now has 250,000 miles and does not burn any oil. I use supertech oil and OEM filter. OCI is 3300 miles. hope this info helps. I would not use any seafoam etc. just change the oil between 3000 to 5000 miles. use a good filter.