The natural context for an examination of this line is this classical radio game:
Z.Nilsson-Hoen, Radio game Norway-Sweden 1970
1.e4 e5 2.Nf3 Nc6 3.Bb5 a6 4.Ba4 b5
When this game was played I believe the radio games attracted a little less attention than they did in the 1950s and 1960s. But still a game against our neighboring country held a lot of prestige.
5.Bb3 Na5 6.Bxf7+!?
Interestingly this brutal attempt at refuting the Norwegian variation is called the Swedish variation (even before this game, I think). For his bishop White gets two central pawns, two checks and a lead in development.
6...Kxf7 7.Nxe5+ Ke7 (Dia)
Obviously Black's king will be stranded in the centre for some time. In addition Black's knight on a5 is out of play and somewhat vulnerable as is his rook on a8. Is this sufficient compensation for the bishop? Only analysis and practical experience can tell. For the moment few players seem willing to take the White pieces but it's really hard to tell as there aren't many advocates for 5...Na5 either.
This is White's most direct attacking attempt. Also 8.Qf3 and 8.d4 are dangerous moves which Black must be prepared for. In addition there is also the surprising 8.Nf7?! with the point 8...Kxf7 9.Qh5+ g6 10.Qd5+ Kg7 11.Qxa8. Fortunately for Black it seems that the queen is completely out of play after 11...Nc6. There appears to have been a postal theme tournament with this variation in 2003. As could be expected White scored badly but the games seem to have been of a rather low standard and may not prove much.
Hoen is armed with Norwegian preparations. The next few moves are according to analysis by Zwaig. At the time when the game was played 8...Nf6?! was considered to be the main variation (8...Bb7?! appears to be untested and after 9.Nd5+ Bxd5 10.exd5 White seems to have reasonable compensation) 9.Nd5+ Nxd5 (9...Ke8!) 10.exd5 Qe8 and now the Swedes had improvements over Schlechter's old analysis which started with the moves 11.d4 Kd8 12.0–0 d6 13.Bg5+ Be7. I am not sure exactly what the Swede's were planning but have been told that the line probably can be found in 'Collijn's Lärobok'. It may well have started 11.0–0 Kd8 12.Re1 Be7 when quite remarkably all the three d-pawn moves 13.d4 (which is likely to transpose to the 11.d4 line), 13.d6 (with the tactical point 13...cxd6 14.Qf3) or even the modest 13.d3 (which takes away a square from the knight on a5) make sense and give White reasonable chances.
It's worth noting that a few years later Hoen played 9.d4 as White against Zwaig: 9...Kd8 10.Qf3 Nf6 11.Nd5 (11.Bg5 Be7 12.Nd5 Rf8 13.Nxe7 Qxe7 14.0–0–0 Bb7 15.Rhe1 Kc8 16.Qh3 Qe6 =+ Hoen-Zwaig, Oslo 1973) 11...Be7 12.Bd2 Nc6 13.0–0–0 d6 14.Nxc6+ Qxc6 15.Nxe7 Kxe7 16.d5 Qc4 17.b3 Qc5 -/+ Kudriashov-Guseinov, Azov 1991.
9...Kd8 10.Qf3 (Dia)
Apparently this rook sacrifice was Zwaig's new idea. I don't know how bad 10...Nf6 would have been.
11.Nf7+ Kc8 12.0–0 Nf6 13.Nxh8 Nxe4 14.d3 Bxd5 15.dxe4 Be6 16.Qg3 Kb7 17.Bf4 Rc8 18.a4 b4
Around this point Fritz and Rybka start to appreciate Black's resources.
19.Be5 Qh5 20.Bxg7
20.c3 Nc6 21.Bf4 Be7 is not better.
20...Bxg7 21.Qxg7 Rg8 22.Qf6 Bh3 23.g3 Rxh8 (Dia)
Finally it's clear that Black is better. I assume the rest of the game was quite pleasant for the Norwegian audience, who must have suspected that Black was on his way to victory even if no clear variations could be calculated.
24.Rfe1 Re8 25.Qf4 Nc6 26.c3 Re7 27.Re3 Ne5 28.Qh4 Qxh4 29.gxh4 Rg7+ 30.Rg3
A bit disappointingly there will be no mating attack.
30...Nf3+ 31.Kh1 Rxg3 32.hxg3 b3
Quite frequently a rook and a pawn can be a good match for two minor pieces in a simplified endgame. But here there is no way to activate the rook and the kingside pawns can quite easily be blocked.
33.a5 d6 34.Ra3 Be6 35.Ra1 Nd2 36.Kg1 Nc4 37.Rb1 Nxa5 38.f4 Nc4 39.Kf2 a5 40.f5 Bf7 41.g4 a4 42.h5 (Dia)
I suppose most listeners had already found the decisive idea:
42...Nxb2! 43.Rxb2 a3 0–1
Addendum March 20th
A quick check in the 1903 edition of 'Collijn's Lärobok' reveals only this relatively short variation after 6.Bxf7+: 8.d4 Nf6 9.Bg5 Qe8 10.f4 Kd8 11.0-0 Be7 12.Qe1 Nc6 13.Nxc6 dxc6 14.c4 with an advantage to White according to Svenonius. Later editions may have had more detail but possibly it's Svenonius' original analysis I should try to locate.