As an owner of the first generation FZR1000 since 1988, I think I have some ability to speak as to the stock setup. The '87 engine RWHP was 122 on the dynos of the day, a bit more than the VMax was capable of (a VMax of the same time was 119 RWHP), and with an experienced rider were capable of turning well-into the 10's in the 1/4 mi. Supposedly, in 1988, Yamaha changed the cams to greatly boost midrange, which smoothed-out the two-step powerband the 1987 model was famous for, but it knocked-off about 10% from maximum RWHP. For most people, this was much more accessible, and made it more pleasant where 98% of riding is done.
To me, it looks like a very clever setup where the stock frame is used, but with different frame loops fabricated in-place. This allows all the engine mounting points to be used, and the gas tank would fit perfectly. The neck does appear to be significantly raked, although I suppose it could come from the triple trees instead. To me, it appears the steering head had a triangular piece welded-in to kick the bottom race way-out forward. If you look at one of the last of the 'under-fabrication' pics, you can see where the piece may have been added, it looks like like maybe 2.5". In any event, it is a slick package, and probably weighs less than the 476 lb. dry weight of the original. Let's call it that weight wet. That makes it 4 lb/HP w/o rider so it should make for a very spirited ride.
Drawbacks I see are the way your legs would be folded-up under you to shift/brake, the extreme forward lean to the handlebars will have a strong man crying after a half-hour in stop & go traffic, and as for the brakes, the bikes were overbraked in the rear stock, and would lock up the rear wheel easily because of the extreme front weight transfer, maybe that would be helped some by the extended wheelbase. The six pots(three opposed) X2 front brakes would probably result in warpage quickly as the disc wouldn't be able to shed heat from that setup quickly-enough. Still, if it's a "t-t" ("tavern to tavern) bike, maybe it won't get that much hard use anyway.
All-in-all, I can appreciate what the builder did here. I would love to thrash it for a few days, but I don't think it would be very much fun to live with. Like one of the bike mags said, recently: "like living with a supermodel, only to find-out she bathed once a week, and didn't brush her teeth."
Still, if you had one of these stock FZR1000's and had this next to it at bike shows, I think the two would complement each other like a flagon of Dortmunder Stout and weiner schnitzel with garlic and herb baby red potatoes. Maybe not to everyone's taste, but appealing-enough if you like the cuisine. After-all it has probably twice the HP of those 836 cc-kitted SOHC Hondas which were everywhere in the early '70's, and lighter to-boot. Think of it as an homage to the inline four chopper movement of the early 1970's. One thing for sure, it gonna handle far-better than any AMEN Saviour-framed SOHC Honda hoped to handle!