Viragos have gotten very rare and I've grown old and bored. Bores larger than 99mm will be special order and have a two month (minimum) lead time. Strokes beyond 75mm the same. Both of these are untested and will require some engineering; costs will be reckoned on work. Currently, I see a maximum bore of 105mm at 81mm stroke for 1403cc. Even this will require some stops and starts in development
Bored and stroked motors will require balancing and improved oil flow. For a 106mm by 84mm setup, all reciprocting and rotating parts much be shipped back and forth to a specialty machine shop/foundry. Costs would be $2400 for the top-end -re-sleeved barrels; Nikasil on aluminum; big CP-Carrillo piston kits with ceramic crowns and treated skirts. For the crank: $2300 for stroking, lightening, shorter rods, balancing, improved oiling, and new main and rod bearings. Reckon on about $200 for dowels, gaskets, seals, and venting, Maybe another $200 for an oil cooler kit. This leaves you with the need to bore out the case spigots to accomodate the larger sleeves. You may want to have your cylinders 0-ringed to hold in combustion.
Blowers: I no longer see mysef developing a kit. If you want to give it a try, I handle the blowers themselves, pulleys, inter-coolers, belts, "sneeze" valves, other bits.
EFI: I've done a lot of reseach but see no cost effective way to set it up. The same with ignitions. I recommend the Igniorg. I developed most of an LED-triggered, front cam set up (using a MicroSquirt), but I can't find a fabricator to make inner cam cap pieces for it. Nor could I see a safe way to keep the cam from moving laterally when it goes under and out of load. Venting I am just too tired and lazy to work on.
Compression releases? My idea is a TT/XT/SR500 style release that hold the exhaust valves slightly off of their seats. Solenoids mounted to the exhaust rocker covers would push down on the valve end of the rockers. Both cylinders. Pushing down as long as the starter button was depressed. Disconnecting a relay (probably by way of a toggle switch) would take it out of circuit and allow the engine to turn without its intervention,
Converting shaft-drive motors to chain or belt-drive? It would be cheaper to buy a more modern twin. Hard parts are no problem, except that at least half of the part numbers are no longer available. In some cases a left-side assembly is available, but not a right-side. Sometimes they can be modified and reversed. Sometimes you must search for a useable old part.