R3 Alternator is good for 37A @ only 2000 rpm!!! (41A @6000 rpm)
Std continuous draw is going to be in the ~ 18A region (not counting momentary loads like fan, signals, brake light, horn) so there is a TON of overhead - and even 150W is another 12A so well capable of adding that.
I'm with 'Bull though - you can get some good high output LED Aux lights these days - I would suggest that the Krista from Clearwater is going to be a useful addition (3000 Lumens, 30W each) - each one of those is approx equivalent to a single 5.75" JW Speaker 8630 on high beam! - or even Darla (2000 Lumens, 24W each) - equivalent to a JWS 8630 on low
And if you couple these with some Daymakers/JWS, you're saving a bunch of watts there already anyway.
Note that Clearwater now has an even BRIGHTER lamp Bull - the Sevina - a massive 7500 lumens, 70W per light.