Drained the system again - definitely felt the chemical additive on my skin - silly me didn't put the "surgical examination" gloves back on

Then I unbolted the dynamo, took out the water pump (which had a slow leak at the lower gasket face), took out the rad (and back flushed it - loads of brown water came out) and then attacked the engine block with the Karcher that I borrowed from my youngest brother (in the late 70's/early 80's he had 2 Minor vans). Water everywhere, loads of brown crud came out of the opening the water pump fits on, but nothing from the cylinder drain hole

Tried the pressure washer directly into the drain hole - even more water everywhere. Totally soaked by now.
Got out the Lidl Endoscopic colour camera and poked it into the cylinder block through the water pump hole - very nice view of clear channels, then submerging int eh vicinity of cylinder #4 - the front of the car is parked slightly uphill on my drive.
Also tried to look (again) into the drain hole - camera doesn't go in very far because of the restricted width, but could see something that looked a bit like a pice of wire - has someone been here before me?
Made up a solution of Caustice soda, got a tube (that could fit tightly into the darin hole, fitted a funnel to the other end and poured some in - no reaction

Put some into the block at the water pump end - no bubbling.
Decided that the "block" must be very localised at the tight corner at the #4 cylinder end and the drain hole. Time to refit the pump, for now and circulate some plain water, drain and then refill with anitfreeze. Before doing this, decided to get a brand new water pump, form Camberley Autofactors, less than 1 mile down the road from me.
Got pump, some 20/50W oil (another thread where I had refileld with 30SAE Comma oil), plus some more Comma SAE 30 oil to use in the gearbox.
Got everthing back home. Applied "liquid gasket" to both sides of the water pump gasket supplied with the new pump. Fitted the pump and got the pypass tube up the bypass hode OK. Bolted on the dynamo and then started to fit the waterpump plulley and fan blade - disaster! The new pump (for 1098 engines) now sports M6 threads on the spidle flange. Camberley Auto factors only do a very small selection of odd nuts and bolts. Down the road to Halfords - they had a larger selection but I was not prepared to buy 2 bolts plus nuts per pack (4 bolts needed) where half the length of the bolt would need cutting off and the nuts are not required.
I'm going to have to go go to a specialist tool supplier (who also does screws and bolts) about 3 miles up the A30, or to a family owned Hardware store over in Fleet - I'd best ring round first. No best please, but at least I have dried out now.
Are all new pumps like this?