As mentioned, you'll be better off porting the heads you've got. Personally I wouldn't upgrade from -1's to -13's I'd go for at least B1-MC's.
Again this has been mentioned but, you will need new pistons as the valve reliefs are bigger and in a different place, also I'm not sure if the headers will swop over either, the -13's are cut back some along the exhaust side face. Also you would be better off going to the 3X intake as the others don't seem to have a lot of material to match the roof of the intake port. For the gains I'm not sure it's worth it.
If and when I get round to upgrading, B1-PSO's will be on the top of the list.


'74 Challenger..9.46 @ 145.9 1/4, 6.001 @ 118 1/8 so far. 4023lb !!! # N/A, Marsh performance 655ci, Indy Maxx, T/R, Indy 600-13 X's, Street legal, pump gas, full interior, Cal-Tracs, mufflers, 3:73's and real 10.5 radials.
9.51 @ 142.4 1/4, 6.003 @ 114 1/8 with our old mule KB, 572-13, 580 wedge.
RHD '68 Barracuda Fastback 323ci street/strip. Best ET 13.88 @ 99.03