I have the sidewinder heads from marsh performance. I hear they are the same casting. I got them bare with valves for $849 iirc. My head porter traded me some work to build them so cost for me was 1200 ported with good springs locks retainers.
They have roughly the same potential as a rpm if you plan to port them. They seem to be a good quality aluminum and a good casting.
My porter did mention he thought the short side was shorter than a rpm, kind of like a 516 head.
But I’ve seen Duane and others on here say these are the easiest head of the budget ones to get 300cfm.
I go straight to a better head if the port work wasn’t free. By the time you put all the work into these you’re only 2-300 dollars less then a trick flow. To me these days just getting trick flows is a no brainer for this category of performance heads.