Just quick question, I was told that there were different callipers to suit boosted or non-boosted 7.5” cooper S brake systems. Other than the trick 4 pots, I can’t find any references to this. Anyone know if this is correct?

If you are talking original BMC factory calipers and not aftermarket then they are the same part whether boosted or not.

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ex-NSW Police 1970 MK II Cooper S
VMCI #43

The originals 7.5" S were all Lockheed (replaced years later by AP) and there are also aftermarket ones sold now. Dimensionally all the same.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Ok, it didn’t sound right to me, and couldn’t find any different aftermarket options. Thanks.

I thought all 7.5" were boosted, un-boosted were 8.5"? In the UK they when they had to go duel circuit and therefor drop the booster they went to 8.5" to compensate. first seen on the 1275 GT in about '77 I think and then all Minis from about '84 onward?.

I stand to be corrected on that though!

Unboosted from the factory was 8.4” and these need 12” wheels to clear

They also fitted them here to the 1275LS

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Yes 7.5 discs were all boosted, however many folks on road and track don't bother with a booster. I drove my Mini wasaMatic for 25 years without one, only put one on because I got sick of looking at my vh44j sitting on the shelf.
At my current age I do now appreciate having one.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Doc, what do you reckon about these aftermarket boosters on eBay and elsewhere? They look ok and are a really good price, get good reviews.
https://www.hemiperformance.com.au/shop ... -rear.html

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1972 Mk3 Mini 1000, 1150cc supercharged.
https://www.ausmini.com/forums/viewtopic.php?f=3&t=95872

They are cheap and do work, but last time I looked they were lower output pressure than a PBR VH44J.
A friend put one on his '1275 LS' (in a van) and he's happy.
I do worry about how well made they are.. your life is in their hands.
Better to find a genuine one and get it reconditioned, IMO. The local brake shop did mine.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.