They still have LT-40s at Nitroplanes. It is the same plane that you would have bought from SIG, just "misdirected".

I learned to fly on my PT-40 trainer with an Aviastar 53 but later changed to just an Irvine .40. I found the extra power of the .53 was just wasted on the trainer. Admittedly the Irvine is a premium engine but it doesnt make the power of a .53. So Idont believe in overpowering a trainer, it may get you out of trouble quicker but it can also get you into trouble a lot faster. Just my opinion based on my personal experience.
I think the Tower Trainer 40 MKII ARF is a good quality kit and the price is excellent. Ihave not flown mine but the build quality looks good.
A light .60 size trainer with a stout Thunder Tiger 46 should work pretty good depending on the weight.