I can't talk as a personal experience becausa, as I told you, I'm looking for such an engine myself. Still, I have seen cars with that engine (well, not the 1.3 from the TS but the 1,4 from the TX) that have both 63 hp and the difference is very considerable. In fact, just the change of the standard 1108 cc from the R4 to the exact same engine in the R5 gives you an extra 11 hp. Just that is a difference.
Im gathering the material to change my engine but it's very hard to find the engine. I have already the webber double carburator, the admission and exhaust pipe and the 5 speed gearbox. The engine, still looking.
Found some in spain but in vary bad conditions. In Portugal I already foud several TX but I refuse myself to wreck a car with documents that can still be saved. The tx is already a classic rare car.
Are in in Portugal? Where? Add me to you messenger (rpecruz@gmail.com) or mail me so we can talk more.
Cheers!