It is good that you have found the errors before you start. I have a close to finished Springbok with the blowdown holes in the frames in the wrong place, i.e., as in the plans. I have to tackle it soon and it will be a difficult and ugly fix. I am not sure how much trouble the front bogie is yet. I should take it to the club and push it round the tightest curves. I have just fitted stiffer springs. The specified ones are a joke. I am dispensing with the steam brake and will fit lead under the cab, as it is very front heavy, with massive cast iron cylinders.

I did a lot of CAD and valve gear simulation. I worked out that as designed, in full gear, there was only about 65% maximum cutoff. Also, there was about 26 thou lead, which I wanted to get rid of. I made a longer expansion link (actually had it and the die wire cut), and with the generous help of Don Aston, re-jigged the valve gear slightly to get minimal lead, and 75% cutoff in full gear. It now must be timed as per the simulator results, not to have equal leads, or the valve events will suffer badly. I want it to notch up smoothly, with no large disparity of cut offs between the front and rear of the cylinders, throughout the range. I have beefed up the reverser stand, and fitted a two start screw, a thing I consider essential.

I have made no attempt to make the design more correct for a B1, as that information which you have before you start, was unknown to me. Anyway, I am not a fine scale enthusiast but more in the LBSC mould, where performance is more important than scale correctness.

Springbok does not have an axle pump, so if you are one of those people who don't seem to be able to live without one, you might want to design one in.

Doug Hewson was going to design a correct, scale B1, and a GA is on the net, but whether he ever gets round to such a mammoth task I doubt. All in all, I would agree that Springbok is a good beginner's tender engine, with outside cylinders, simple boiler shape, welded (no rivets) tender, and simplified detail.

Two start means that there are 2 threads on the same rod spaced 180 degrees appart. The advantage is that you have twice the surface of the thread available for thrust and that the pitch of the thread is normally coarser. For the reversing stand it would mean that you did not need to turn the handle so many times between forward and reverse. Downside is that at that scale, you are talking about some very neat screw cutting and possibly sourcing a two start tap?
BobH