A subject close to my heart!
I have just looked at a picture of your DB8 on Chester's website and I think that you will really struggle to convert your existing lathe.
The problem is design; your Chester will need an access for the belt to the headstock and this will require a countershaft in the position where the electric motor is. Unless you get your gearing right you will stuggle to get speeds of any use.
Why not keep that as it is and get an existing treadle lathe for when the power gets turned off?
I have several Drummond lathes and I have three 3 1/2" flatbeds that are complete with treadles; a 1907, a 1914 B type and a 1927 longbed M type. Treadling is HARD work, especially if you are screwcutting, as you are driving so much resistance through the changewheel gearing. It can be done though, and was, by everybody who used small lathes (up to 6 inch centre height) throughout the 19th century and into the 20th, who had no lineshafting (my great grandfather who owned my 1914 B type which he got in 1916). Just look at how many lathes were sold with treadles.
One of the tricks though is to have an apprentice…there were the ones who treadled while the master did the work! Have you got grandchildren? Everyone these days complains about kids not getting enough exercise.
Incidentally, the 1907 flywheel weighs half that of the B and M types, and being a lighter lathe, may have been so designed to reduce the amount of hard that the operator may be tempted to try. The later B and M type beds weighed twice as much and the M headstock can take a phenominal cut for such a small lathe. I mainly use a motorised 1948 M that came from the de Havilland works (still has the works plates on) and, just for a one off experiment, cut 1/4" of cast iron in lowest backgear with a carbide tip on a facing cut. I don't know if any of you would dare try that on a modern lathe of the same size?
There is a booklet, produced by Drummond in the early 20s, that demonstrates the work done by amateur craftsmen and has a 9 cylinder radial engine entirely produced on a treadle Roundbed, with some of the setups used. If they could do it, why can't we?
My point is: get another lathe, one that was designed to be used with a treadle, rather than try to convert a modern shape lathe.
Just another point; pitmans. I have both types, slotted and round. Both have merits. the 1907 has a round pitman with a bush, the 1914 has a slotted one and the 1927 goes back to a round one but with a ball bearing. I suppose that it comes down to the price of ball bearings, that the cost of manufacture was reduced significantly during the First World War.
It is not my intention to inflame the ready (pointless) debate about the merits of this or that machine tool, I am just pointing out the old chestnut "horses for courses". Anyone can use whatever they want or can afford and I don't care; I am happy with what I have got.
All the best,
Andy