I’m by no means an expert on your car …..
But might suggest a method my father used back in the day… He was a mechanic for several manufactures back then.
In the 60’s and 70’s the way they would de-sludge an engine.
Step 1
A) Disconnect the battery
B) Drain the engine oil
C) Mix 3 quarts kerosene and 2 quarts(cheap)oil
D) Pour directly into the crank case via the dipstick tube
E) Let sit for 30 – 60 minutes depending on the amount of sludge present
F) Shake the car repeatedly for a few minute to allow the mixture to wash down the crankcase and oil pump pick up tube
Step 2
A) Drain crankcase
B) R/R oil filter with inexpensive one
C) Mix 2 quarts kerosene and 3 quarts(cheap)oil
D) Fill crankcase as normal
E) Disconnect ignition and fuel delivery
F) Connect battery
G) Crank engine several times to circulate the crankcase mixture
H) Check dipstick to see condition of cleaning mixture.
I) Once satisfied Drain crankcase and remove Oil filter
J) Leave drain plug out, open oil fill tube, pull dipstick and allow to vent for ~30 minutes
You can also use an air compressor to pump air into the crankcase
Step 3
A) Reinstall drain plug and install new (cheap) oil filter
B) Reconnect ignition and fuel
C) Fill crankcase with required amount of (cheap) oil
D) Start and drive car for a day
E) Drain and refill oil and replace oil filter of your choice
I know some may question this old school method, but I’ve seen it done many times