Hmmmm...I see a sudden,unexpected run on 700 Interceptor engines,parts and components on eBay...I'm no psychic,but if it's that easy...why throw a fortune at a modern 500 Bullet single engine...throw the same money at a Interceptor engine,and have something UNIQUE...too cool...
It's because if you throw alot of money at a Bullet 535 or 612 single, you get very close to the hp of an Interceptor, and still get the 100+ pound lower weight advantage of the single.
While some claims were made for a high-13's quarter mile for the Interceptor, most averaged in the mid-14's for the quarter mile.
There have already been Bullets that have posted in the high 14's for the quarter mile, and it may be possible to get to the mid 14's, which would put it on par with a typical Interceptor. In any case, it could get very close, and be lighter and nimbler.
Also, if you read most Interceptor road tests of the old days, the company "claimed" 115mph top speed, but most tests showed maybe 103mph-106mph as what they actually could do.
There are modified Bullets that have done 103-106mph or more out there right now.
Add to that the fact that it costs more to build an Interceptor engine because there's 2 of everything to buy, and the vintage parts aren't cheap, and you end up with reasons why people hot-rod Bullets.
You get comparable power and speed, in a lighter package, and the cost is comparable too.
In fact, the Interceptor is the most powerful version of the big Royal Enfield twins, and the 700 Super Meteor and Constellation have lower power, and they can be virtually equaled by a hot modified Bullet for power.
Plus, I personally think the Bullet engine is a better looking engine, anyway. The vertical twins are too "fat" looking for my taste.
The thing that's better about the twins is that they are bigger, so that they will produce their power loafing along, but you have to push a modified Bullet to do the same results. So, it will be easier on the engine for the big twin.
A cheaper way out is to drop a Yamaha XS650 engine into a Bullet frame, and get alot of power for only a few hundred bucks. But then it's a Yamaha, not a Royal Enfield anymore.