Chris,
All the Spitfire (and all Herald derivative) suspensions work from the same
main principle, with some specific differences.
The common factor is independant rear suspension - the differential is fixed
to the chassis, and each half-shaft pivots about the diff (using a universal
joint) to give the wheels up-and-down movement. In all cases, also, the
load is taken by a single, transverse leaf spring - effectively a long,
bendy bar that is fixed to the differential in the middle, with one wheel
supported by each end. Finally, they all have radius arms - horizontal
beams running (more or less) fore-aft, with the front attached to the
body-tub behind the seats, and the rear near to the wheel hub, to allow the
wheel to move up and down, but prevent it moving fore and aft.
Early Spitfires (Mks I to III) had the leaf spring fixed rigidly to the top
of the differential, so that when one wheel moved up and down no load was
transferred to the other wheel. This was the design that suffered from the
notorious 'wheel tuck' - under hard cornering the inside wheel would drop
right down, and if you then suddenly turned the other way all the load would
go on this tucked wheel, and the car would oversteer big time. There is a
perfectly good fix for this, the 'camber compensator' developed for racing,
which Joe Curry (on this list) will be able to sell you. Check his website
for more details, and a better explaination of the problem:
http://home1.gte.net/spitlist/CamberCompensator.html
With the release of the MkIV (the first 'squaretail' Spit) Triumph had a
solution for production - the 'swing spring'. In this design, the leaf
spring is not rigidly fixed to the top of the differential, but instead can
pivot a bit, so that if one wheel is loaded then some of that load is
transferred to the other wheel, which will therefore maintain a firmer
contact with the ground. This fixed the problem. The down-side was
slightly increased roll, but this can be fixed with a stiffer anti-roll bar
at the front.
Part-way through MkIV production there was a further modification, with the
rear track being slightly increased, using longer half-shafts. This design
was carried through into the 1500.
GT6s I am less exact on. They may have had the same fixed spring design to
start with, but that was soon modified to the 'rotoflex' design - this
modified the fixed spring approach by adding a second flexible joint at the
wheel end of the half-shaft, and a lower wishbone, so that the wheel always
remained perpendicular to the road (for the Spit the wheel was always
perpendicular to the half-shaft, so as the wheel dropped the bottom would
move inwards as well). They might have been Rotoflex from the start. From
the MkIII GT6 (equivalent to the MkIV Spit) they used the same swing-spring
as the Spits.
Basically, you are fine whatever model you go for. If you get a round-tail
Spit you would be well advised to fit a camber compensator, if you get a
square-tail then it will be fine just as it is. If good suspension and
handling is important to you, it would be worth stripping down and replacing
all the old rubber bushes with nylon, and probably replacing the rear spring
as well - they tend to sag with age, and only cost #60 ($90) or so in the
UK.
On the subject of engine swaps and originality, you will find a diversity of
opinion on this list, but, more importantly, absolute tolerance of everyone
elses opinion. There are those that like to keep it original, but they are
supportive of those who, for instance, have stuck a Honda S2000 or a big
Detroit V6 under the bonnet. I haven't heard of the swap you suggest, but
we'd all be interested to hear the outcome!
Good luck finding the Spit of your dreams, whatever Mark, and if you want
any tips on what to look out for, how much to pay etc. etc. just ask here!
Richard & Daffy
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