Turing machine update
Paul Rendell has now completed his Universal Turing Machine, by adjoining two stack constructors to the bounded version of the pattern. The patterns are available here, including the c/2 orthogonal and c/5 diagonal variants of the pattern.
The new Turing machine emulator is period-23040, which makes it more HashLife-amenable than the previous UTM and TM emulators (p18960 and p11040, respectively). Additionally, the diagonal stacks run faster in Golly than the oblique analogues. The c/2 version outperforms the c/5 version, apparently, despite having a larger growth coefficient.
This is the first universal computer in Life to emulate a Turing machine in linear time (Chapman's URM takes exponential time; my UCC takes quadratic time), and therefore the most efficient to date.