When welding g alloy it gets a bit bright, we use marker pen either side, on ships I've seen people use French chalk, either side. You could try a lighter shade, I use 9 on steel, 10 or 11 on stainless and alloy. How close you put your nose helps, but it is called a dark art for a reason. Practice,practice,practice. You'll get the feel for it. :-)
Can of worms time here, Len. Type E box has 23 splines on a 1" shaft, Type 3 box has 20 splines on a 7/8" shaft, Clutch plate and spigot bearing would need matching up. Gearbox mount may require moving or modding, clutch actuation may need modifying to. Saying all that, it is basic engineering, and possible. Avery good article is this one: http://www.dominicbolton.freeuk.com/articles/ford_gearboxes.pdf I have read this t many times ! good info about ratios etc. Performance?? hard to answer that one, without knowing what you want to do with it. Hope this helps.
27 years, that's impressive! I hope that you have still enjoyed owning it and dreaming of the day. I have spent many more hours working on mine than driving it and a lot more time than that thinking about it and planning. The driving is only part of it. Post some photos when you get a chance.