Thank you all for your thoughts and advice; I like SSsssteamers idea on the Stanley steam line swivel so will look out for one to copy.My thoughts on needing flexible hoses to the engine was to avoid fracturing hard pipe connections due to any engine movement and yet to allow for enough movement for adjustment of the chain tension. Would the Stanley swivel cope with that?

I was out with Bob Dyke yesterday in his 1902 baby White and this time we fitted a temperature sensor to the steam line. I know White boilers are monotubes but the working temperature range quite surprised me as we went from 350F up to 960F ! The pressure also varied considerably from 150 to 500psi.It wasn't running too consistently and Bob changed the main jet size once and adjusted the temperature control valve as well. All seemed a little hit and miss though quite "challenging" and the run gave Bob some indications of what he has to do thsi winter.
My Stanley type boiler is not going to get anywhere near Bob's temperature or pressure and I would hope that it would be more consistent by having a reserve of steam.

Jeff, though I posed the question of what limits my lightweight Toledo's speed from achieving 50 mph --boiler capacity, burner output, mechanical strength or all three--I didn't mean to give the impression that I wanted to achieve that speed. As you rightly say steering a straight line with a tiller steered car and stopping it above about 35mph will be more than enough of a challenge! But if I am to tackle my objective of re-running Oliver Lippincott's attempt to cross the Rockies in my car in 1902 then I would like to be able to know or calculate what the limitations on steam generation will be be with the layout that I am planning.

Nick