I think the weaponry proposal suggested by You is reasonable. To hit something in a deflection shot requires two points:
1.) a reasonable flat trajectory to ease aiming
2.) a good volume of fire.
The P-80´s 0.50 cal M2 (no M3 prior to the late 40´s installed in P-80´s) is a uniform, 6 barrel arrengement (= 80 rounds per second).
It has a muzzle velocity of 870 m/s. and an avg. rate of fire of 800 rpm + one of the finest ballistic properties. The 48g. projectile will drop below Mach 1.5 according to RG at an estimated 900m distance (at sealevel, without taken plane speed into consideration). At 300 m average firing distance, it will have a remaining velocity of 736 m/s. We therefore may conclude that the conditions for 1.) and 2.) are fullfilled perfectly.
Regarding the volume of fire, we should note that at any given time at 300m distance, the mean distance between the projectiles is 9.2m. for the .50cal BMG and the time elapsed between two succeeding hits at this condition is 0.0125 sec. For a very bad high angle (near vertical) deflection shot a plane moving at 166 m/s (~600 Km/h) may result in a .50cal hit each 2.08m (averagized). Assuming some perfect aim hold, a 10.6m long fuselage will receive approx. five 0.50 cal. BMG hits.
Now let´s turn to koolkittys proposal:
The 2 MG 151/20 have a muzzle velocity of 785 m/s. and a rate of fire of 750 rpm (= 25 rounds per second, total). According to RG the 20mm mine round will drop below Mach 1.5 at 250m. At 300m distance, the remaining velocity is 530 m/s, equaling to a mean distance between each round of 21.2m for the 20mm mine rounds and timeframe of 0.04sec.
Using the same high angle deflection shot as above a 10.3m long target (approx. P-80 sized) moving at 166 m/s. may encounter a 20mm hit each 6,64m. Therefore 1.5 mine hits may be expected here. (barely sufficiant to ensure You hit something at high angle deflection shots)
The 2 MK 103 have a muzzle velocity of 860 m/s and a rate of fire of 420 rounds per minute (= 14 rounds per second for two guns). The mine round will drop Mach 1.5 at ~600m according to RG. At 300m distance the remaining velocity is 662 m/s. (Ausf. A mine round with poorer ballistic properties) and the mean distance between the projectiles is 47.3m (!) with a timeframe of 0.071 sec. between two succeeding hits, equaling to a mean average distance of 11.8m. We therefore would only expect 0.87 30mm hits, which is not enough to ensure that the P-80 get´s hit at all, altough the probability not to hit the P-80 is very small (five out of six passes will hit).
So You have five .50 cal. hits vs. maybe one and a half 20mm and perhaps one 30mm hit...
-of course, the 20mm 30mm mine rounds are MUCH more severe to the P-80 than is the .50 cal API to the -262.
To put this in prospect, the normal, four 30mm MK 108 equipped Me- 262 A1a will result in between 2.65 and 3.5 hits, depending which version of the MK 108 is used, -low muzzle velocity is not always a disadvantage when it comes to compare the volume of fire! But then again, the low ballistic property of the MK 108 will make deflection shots impractical as an event.
My favourite armement would be three MK 103 put into the nose. That gives uniform cal. armement (easier to aim with), good ballistics and enough volume of fire to ensure hitting a target even at the worst possible deflection shot (1.3 hits). A 30mm mine contains about 7.7 times as much explosive as a 20mm MK V HE-round and still nearly twice as much explosive as a 37mm MK4 HE-round. Such a hit will assure destruction (safing a dud or perhaps a wingtip hit) of a P-80.
RG considered an armement of four 15mm MG 151/15 as optimal. This, too has merits. The weapon installment can be done quite easily (no major modification is necessary and the replacement of the guns can be made on the staffel workshop level), requiring only minor differences. The ammo is both, smaller lighter (166 gramm vs. 480 gramm), too, so more ammunition can used per gun (250 rpg for the lower and 200 rpg for the upper pair). The guns would also free up some 160 lbs of weight in the nose.
The muzzle velocity is very high (850 m/s for the AP 960 m/s for the HEI) as is the sectional density of the projectile (the AP), resulting in an extraordinary flat trajectory, as good or better than the excellent .50 cal., easening deflection shooting. You would expect three hits in our deflection shooting model. The AP rounds would go right through the structure (and are particularely good for strafing against lightly armoured ground forces as well) but the HEI rounds does only contain 2.8 gramms high explosive, nearly three times as much as the .50 cal API but not enough to cause significant blast effects. Therefore, I would not prefer this kind of armement as long as not a useful mine round is developed for this gun (this hypothetical mine round would be around 48 gramms and has comparable blast effects to a 20mm Type 99-2 HE round, fired with a muzzle velocity of >1000 m/s).
The armement would be limited to deal with fighters + ground attack, only. It is a very good armemnt if You consider the R4M for bomber hunting, as suggested by RG or the hypothetical mine rounds as sugested by me!