Briggs cylinder (mag side) bushing- Question

[creia]

1977 Briggs 5HP - horizontal shaft , All-aluminum "Kool-Bore" engine
M- 130202
T- 0135-07
C- 77110710
I recently took this engine into inventory. It was mounted on a Montgomery Wards (remember them?) tiller. During my routine disassembly and inspection, I noticed something unusual, that I have never seen before in over 30 years of working on these engines. It had a steel cylinder bushing (Briggs part # 297565) installed in the mag side aluminum block bearing. I know that Briggs sold these as a retrofit correction for a bearing that was worn past "reject" size. Now, you may ask, why am I saying that this was "unusual" to see this installed on this engine? Read on....

It was evident that the engine has had relatively little use and excellent care:
1. Good compression and excellent leakdown test results.
2. Bore not scored and well within(measured)specs. Some original "crosshatching" can still be seen on the bore
3. Ring gap only .019"
4. All crank journals and crankpin were well within specs.
5. Rod and rod cap not scored and crankpin to rod clearance within specs (.0025')
6. Piston not scored or even scuffed.
7. Sidecover/sumpcover (aluminum) bearing within specs.

I question the NEED/REASON that this bushing was even installed (as a "retrofit", that is) with such a low use engine and everything else beings well within specs?
OK, here is my question: Did Briggs manufacture some of these engines with the steel bushing installed from the factory? Have any of you old -timers ever seen this? Was it a factory done heavy-duty upgrade on some engines for heavy-duty use? In addition, the overall install looked too good for a "retrofit" The notching and staking of the aluminum bearing that is required to keep the new steel bushing from turning looked too perfect, if that makes sense.
Thanks for your interest and I welcome your opinions as always.
Michael

[bgsengine]

Very well could have been done at the factory to fix an error during production, could be done to Monkey Wards' specs, but unlikely to be for "heavy duty" usage - Could have been a QA line pull engine or one that was used in factory training and then sold on to manufacturer.. lot of possibles. I know I have seen some engines with those bushings , most all were quite professionally done , likely by machine shop (typical small shop would not have had the money to put into those very expensive tools, and the precision machine shop stuff needed to make effective use of them, so plenty of blocks would be shipped out to a machine shop that was properly equipped to do that work - just like installing camshaft bearings in a V-8 engine block or some such) I know some engines (typically they'd have been horizontal shaft) could be spec'd with ball bearing PTO end which WAS a heavy duty option , but can't imagine needing bearing inserts in top end except to correct for some sort of error - Got to remember back then in the 70's it would have been well worth the time to rebush an engine block for a specific small batch run for a particular manufacturer's spec, rather than having to order in a new batch of castings from the forge... so I could believe it might have been factory original insert.

[creia]

Thank you Brian.
After reading your reply and explanation, I strongly feel that this engine did indeed come from the factory (for whatever reason) with the steel bushing already installed. I consider this kind of a bonus (and upgrade) in that a steel bearing surface would not wear/score as readily as the original aluminum bearing. Overall the engine is in fantastic shape (one of the best I have ever taken into inventory), especially for a 46 year old engine!
Michael