I don't want to step on other toes, but it is rare, no mater what cleaner or techniques is used, that a new Bosch MAF will take a cleaning without killing it.
As for you ideas around 2 different set ups, don't waste your time trying. Our 50 year old engine can't put out much more power and with the current ECU's, they won't let you try and second guess them.
If you want to do anything, since you sure don't need any more horse power off road, work on improving what you have.
Not to start a ******* war but hear goes;
Sorry Mike I can't believe your above statements as I have hands on. I have more power and torque way more than even the 4.6 had when first installed. Your don't need more HP (?) lower your meds please as these Rovers are already under powered look at the power to weight ratio number, kind of sick my friend.
First off at 72K the guttless 3.9 became a 4.6 for 500 plus miles of working it breaking it in. Ran better than the 3.9 yes. Next the RPI Tornado chip, this woke it up big time. Then recurved the dizzy and added a vacuum advance unit from Oz., way better than the POS from Rover. Then the intake, heads, exhaust manifolds port matched plus MagnaFlow high flow cats with Borla cat back. Another increase of performance. Then the ram cold air you can feel the difference with this as this is a 1 minute swap back and retest. Then the restriction to the hot coolant to the plenum, stupid HP sucking and detonaiton causing problem. I just finished the injector swap to more modern 4 hole Bosch disc units plus the 1 1/2" ram tube extension lift plus the .250" plenum spacer I machined. This last injector with intake extensions project made a difference as much as going from the 3.9 to a 4.6 engine another increase in the fun and run factor. This thing is fun hands down to drive, way better than the stock 4.6. I may stop by and see Mike Green In Livermore Calif. 28 miles from me and let him test drive this D1 again. he drove it with after the 4.6 install. Oh he's Rover trained plus off roads and races. Dump the clutch in 2nd if rolling from a stop in front of a cop then add throttle with normal take offs. This became a way better low end pulling motor, I bet better for off road where low end torque is needed but still hits 5,800 if I want to beat some jackazz in a LR3 which is easy to do plus fun as hell plus I can out corner them. Set up for the street action only. Yes there is a lot you can do to increase performance plus still pass smog tests, it seems 30 years in service hasn't opened your mind to beyond what you have been trained by Rover, kind of sad. Sorry to be blunt I speak with facts. With all respect Mike i'm not belittling you, this is what I have done besides many other secrets to this 4.6 engine with results. My fear is blowing those two spider weak diffs and the 5 speed.
Today I did a 5th gear idle down clean until only compression alone stalled the motor plus I can pull away in 3rd or 4th at 850 rpms or maintain speed in 5th at 30 mph. A very flexible motor now. I swap back to the original MASS 3.9 vs the spare altered voltage 3.9 and the 4.6 unit, reset the TPS then pass smog with ease. Home again to retune for power and fun again within 20 minutes. This I have built would make for one hell of a good low rpm torque motor for off road plus a sleeper on the street that has surprised many of vehicles out of my league. Gas mileage also increased, a win win 8 year project, With your 30 years as a service manager you should tell RPI and Rimmer Brothers that they are making too much magical HP. A 15 year D1 owner 40 years with the 215 motor. NUFF SAID.