You can get the Toleman from the 83/84 Mod by
The 85 Mod by Markus und Vailante (MVC) has the Senna with raised HP Amount that is only suggested as Qualifying Engine but still has room to the insane power it had in real life.
1988 Mod from Carrera.4 has rather iconic predictable physics which either let's you on the track or not but not that much in between without fiddling your settings.
SRM 1990 has the most easy physics around and was mistakable suggested as quality standard which it isn't, despite a decent mod apart from a few nags.
F1SR has Historic 91 and 92,93,94 League Editions around, 91 beeing the best and the hardest at the same time you'll have to put enormous amount of time in your setups.
The 86 Lotus from Senna has been around as single car but originates from a not namingly source for public use, it doesn't feel too right compared to what middle 80s F1 cars would be and deserves quite some work.
You can use rfactorcentral's one click installation which will do the work for you, it's just drag and drop tho so you should definately look into how things link together so you can merge to what you want as Senna Career Mod, Reiza will be doing a Standalone Mod of his Highlights tho so you might aim your eyes at this too
