My 71 swinger has a 7 1/4 rear with 2.76 gears. How much HP/tq is too much for this rear. Was looking at a few 360s, 340hp-401hp, 340 tq-440 tq.

All of those engines have too much power for a 7 1/4. You need at the very least an 8 1/4 axle.

A friend of mine had the later c-clip version in a 93 Dakota 2.5 I4 and broke it. Also had another friend who had an 88 Diplomat with a stock 318 and broke it. Everything about that axle is WEAK

Between my parents, myself and my brother we had 5 different cars with 7 1/4's back in the 90's and everyone of them blew up, all with weak 318 lean burns in M bodies

Randys has 4:10 gears for it (lowest available) & good spiders (a weak point) but as said it'd be money wasted. I would locate an A body 8&3/4 which'd be SBP (& $$$) or a truck/E body 8&3/4 which'd be reasonable (& BBP) & have Moser shorten the housing/axles

A Sure Grip unit will help distribute the load on the spiders so they will take more abuse but they are not available new and are hard to come by used.
Bottom line is they are not worth putting any money into. Baby what you have till you can swing an 8.75.
I'd go with what RR said, a core unit from a late B, a C or a truck, narrow it and buy some good LBP axles.

And all that said, which I agree with, but I owned a 65 Barracuda that originally had a 273 4 speed, followed by a hot 318 4 speed that I drove very hard, still had its original 3:23 gear open 7 1/4 when I sent it down the road.
I believe the single wheel smoke show wiped out more 7 1/4 spider gears that any other cause. Most 7 1/4"s I've seen broken were usually spider gear failure related. Gene

Just making sure. I know a guy that has an 8 3/4 or 2 i,ll have to talk him out of

I used to drag race a 66 dart with mostly stock 360 and 7.25 rears and they usually only lasted a few weeks and yes it was the spiders pretty much every time. I never found a posi in one till I had moved on from that gig.