yea it sounds funny and a wastes of time doing but actcly i got the idea from the owners that have celica gts with the 2zzge i know 2 diff motors but just an idea. and i keep 4geting that cosworth designed the svt enging and header and ect.
it would be a waste cause the ports are not as wide as the openings on the header!! it will do nothing but strain ur time and budget, not to mention you could actually ruin the flow in the header and make it less smooth!!
User itbparada ported his SVT header down at the bottom most portion of the header. Here are a couple of his pictures for reference. I'm unsure of the possible gains by this, if even at all, but its a picture reference. I don't see it hurting anything however, and its all in your patience and time. I'd imagine removing rough edges in the exhaust this close to the exhaust ports would be beneficial though.
Really, its all in your time and attention to detail. But I think the principles of why an ORP outflows an HFC pertain to this aswell, in which any notable restrictions in exhaust flow hinder performance, although this is on a much smaller scale.