Optimum Type 4 for road racing Options

[Charles Freeborn]

Title says it - taking opinions on a competitive T4 used for vintage group road racing. Primary tracks will be PIR (Portland), The Ridge and ORP. PIR is a relatively flat high speed 12 turn track. The other 2 are much more technical - slower, more turns, shorter straights.
Cases need to be EA or EB to qualify for the run group I'm shooting for (F). Currently have a 94/71 with big valve heads, 9.5:1, IDF 44's Webcam 86B. It's sound, but getting tired - showing some cracking in the heads, so if I get another season from it I'll be happy. Prefer to keep CR in the range that can run on pump gas - also durability is a factor.
Some thoughts/questions:
Shorter stroke / bigger bore for better top end? - with current gearing I'm running out of redline on longer straights.
Billet crank from SCAT?
Split Port heads from SCAT?
Mahle Euro pistons or CP or JE.
Nickasil cylinders worth the expense?

Very interested in hearing the specs on any of your builds - how they behaved and how long-lived they were.

Gearbox is a separate issue- will get to that when I've got the engine specs sorted.

Many thanks.