Block Identification - Rover 3500 / 3.5 liter? shim plate?

[buickv8s]

I am having trouble identifying this block after searching on the internet for block casting / stamping numbers.  The intake, timing cover, water pump, and harmonic balancer on this engine are all Buick 215 parts verified by their casting numbers.  But this block is definitely not a Buick 215 block.  There is no pad / ledge at the front where the Buick 215 numbers are stamped.  This block has some numbers stamped at the back on the bell housing "ear."  

Is this a Rover 3500 engine?  Can anyone tell what year or era or size it is by these numbers?

What is the deal with the shim plate behind the flex plate - is this typical for Rover to get the correct torque converter clearance?  Or is this typical for the Buick 215?

Thanks for the help!

[MGBV8]

Early Rover P6.

https://rimmerbros.com/c/Rover-V8-Engine-Numbers

[ag1234]

About that shim, likely used on the Buick 2 speed auto, (air cooled). Cooling air is drawn, centrifugal over aluminum cooling fins of bolt-together, 5 element/ Dual-path, torque convertor.  Air exhaust through elephant ears, on back of block. Otherwise known a baby Dynaflow.                                                                    TMI,  Art.

[buickv8s]

Now it makes sense why the shim is cut back at the two ears - to let more air flow through.  The transmission case matches this shape.