Anything can be fitted to anything, given enough time and money.
However, if you want to achieve your goal while spending only sensible amounts of time and money, perhaps the following bits of first- and second-hand experience might be of use:-
1. Japanese forks with 35mm dia stanchions require only a small amount of machining to the Triumph yokes/triple trees to fit. However, finding forks that would take the Triumph axle might prove too great a challenge. Also, dunno what corrosion problems you experience in Maine but here in GB, Japanese alloy corrodes like crazy and some of their more Heath Robinson swinging and sliding arrangements need stripping at least every couple of years, unless you remake pivots, pins, whatever in stainless (same goes for XS650 brake bits
2. A Triumph right-hand disc slider, second caliper and disc might be the easiest route to retaining the existing Triumph front wheel. As well as Norman Hyde, certainly British dealers like Triple Cycles (www.triples.demon.co.uk
) and L.P. Williams (www.triumph-spares.co.uk
) have right-hand disc sliders; whether your wallet can handle the exchange rate is a matter between uou and it.
One thing you may want to know is that there are two slightly different r-h sliders. Originals have the seal held in with a circlip; certainly L.P. Williams makes the seal holder more like the pre-circlip ones.
You can fit alloy calipers from Lockheed or Grimeca, or match the standard original caliper by fitting another one upside down on the right. Bleeding isn't a problem if you also fit braided hoses, you simply unbolt the caliper from the leg and turn it 'right way up'. Ime, the weight of twin steel calipers doesn't affect the handling.
Lockheed made (make?) alloy calipers with two different piston diameters. The large ones are the same as those in the steel calipers, and it's debateable whether a 5/8" i.d. (single-disc) master cylinder is sufficient - it's possible but you get a lot of lever travel. Lockheed actually supplied Triumph with 7/10" (*not* 3/4") i.d. for twin calipers with large pistons. The alloy calipers with smaller pistons were supplied to Triumph later so that Triumph could fit a 5/8"i.d. master cylinder irrespective of whether the bike was going to have single or twin calipers.
The r-h slider caliper mountings are threaded UNF and helicoiled as standard, so that the caliper can be removed easily for wheel removal/replacement. I recommend doing the rethread/helicoiling to the l-h slider too.
Hoses are much easier if you use the L.P. Williams cross-over tube. This bolts to the lower yoke stanchion clamps and takes a banjo in each end. You then just require a banjo-fitted hose from each end to one caliper and a third banjo fitted hose from one end to the master cylinder; this can be two single banjos on a double banjo bolt at one end or a double banjo on a single bolt. You can also attach a banjo adapter, perhaps on the opposite end to the master cylinder one, to take the proper '79-on brake light pressure switch.
Standard Triumph springs and dampers are poor by modern Japanese standards. Progressive springs aren't too expensive and are a worthwhile mod. on their own; however, to match modern standards, you need the (expensive) damper rods from Triple Cycles.