Some Rifa MKP types :
All PHE420 are 160volts types, and rather large, the 10uF version is as big as the equivalent red Wima MKP10->BIG
imo, the PHE420 is at least as good as the Wima, but used to be a lot more expensive here.
PHE420 has been replaced by PHE426
Unfortunately the marking does not have any alpha designation. I did also a search on Rifa site but they all now sport a designation before the the number. So still I do have the same doubt though I'm inclined to think they are polyester.
More though, I found on my parts bin some beautiful Siemens 4.7u rated at 250V marked MKP (so no doubt on these ones) also on blue plasitc cases which are somewhat bigger than the Rifa's. But Rifa rating is lower so who knows.