Steven: You may have mentioned it, but I'd still like to hear more!
There's a bit of the M60S near the junction that is kind of flared, but there's no equivalent on the M60W. So would I be right in thinking that the plan involved having the M60S mainline cutting the corner to the M60W, merging with a Y-interchange? Access to the M66 and (via the roundabout) the M62 from the south would be via a separate Y-interchange at the flare.
Or do you mean that provision was made for a freeflow link to go through the junction itself, over or above the roundabout?
I'm also curious as to whether any link would require demolition of the minor road bridge over the M60S or nearby residential properties.
Don't forget that the M60 has been widened almost out of all recognition here. You need to look at maps that date to whilst that section of motorway was still M66 (or M68
Back then, there was a huge gap between the carriageways. This, as you have supposed would have had been where the slips from the then-M62 to the west would have landed, and would have become the mainline to the south.
These slips would then have "done a Lofthouse" and landed at a fork intersection a little to the west of the roundabout. The difference to Lofthouse is that the slips at Simister woud have been above the junction not below.
There would have been no property destruction at the time, though the modern housing estate to the NW of the junction would have been a couple of houses smaller!
As it happens, a similar solution would have been employed at M62 W <-> M57 S to the east of Liverpool. It's easier in that case to see where the slips would have met the M62 as the Whitefield Lane overbridge is excessively wide...
I'll add the original junction design to the Might Have Been Map when I get the chance if people would like.