I think that knowing the geometry alone of the Enigma would not be anywhere near sufficient to build a frame that gave a similar feel. I imagine that being a relatively expensive custom titanium frame, it may have used butted rather than plain gauge tubing. So you would need to know the tube butting profile as well as the diameters, and those would only be valid for titanium, because the stiffness of steel is different. Bikes built with the same geometry but different tube profiles/thickness will potentially feel very different, e.g. see this anecdote of 531colin's who designs many of Spa's frames -
viewtopic.php?p=1504658#p1504658.
For the record, be aware that seat tube length and angle probably won't have much impact: the saddle is a point in space linked by the seat post and seat tube to the bottom bracket shell. The saddle can usually be correctly positioned regardless of a degree or two's difference in seat tube angle by choosing a seat post with more or less set back.
I think that the numbers which determine the steering/handling (as opposed to the feel of the frame stemming from the combined effect of the stiffness of the various tubes) are:
- chainstay length (bottom bracket axle to wheel axle)
- front centre (bottom bracket axle to front axle)
- bottom bracket drop (below an imaginary horizontal line joining the axles)
- head tube angle
- fork offset
You might be able to measure all these yourself. I think some smartphones can measure angles (but take two measurements - the second one with the bike rotated 180 degrees on the same piece of floor, taking the average of the two measurements to eliminate any error from a floor which is not completely horizontal).
Small differences in these numbers are unlikely to make a significant/especially noticeable difference, and moreover I doubt that the numbers for your frame are unusual (unless you have particularly unusual body dimensions).
It looks to me as though your Enigma took a fork with a 1 1/8" steerer. The market has changed a lot in recent years, and there is much less choice of such forks for rim brakes, and probably fewer still (if any) with mudguard eyelets. It is now fairly common for carbon forks to have tapered steerers, necessitating a larger diameter head tube. The vast majority of carbon forks are made for disc brakes, and you may be much more likely to be able to find a suitable fork with mudguard mounts if you have a front disc bake as well.
Assuming a carbon fork, head tube length is arguably a matter of the length being sufficient to get the bars/stem high enough without an excessive number of spacers under the stem (most carbon fork manufacturers stipulate a maximum of 30mm of spacers, and some manufacturers also stipulate a minimum of 10mm - making the tolerance somewhat tight and making it necessary to choose a stem with suitable rise to provide any more adjustment. Note however that two forks with the same offset might have quite different A-C measurements (axle to crown), i.e. a 10mm shorter A-C measurement will slightly steepen the head angle and might warrant a 10mm longer head tube.
I can't help thinking that you are setting yourself up for a lot of headaches, and potentially disappointment as well, in trying to 'reverse engineer' your Enigma.