Full size drawings are available from several sources in England. I purchased mine from Blackgates. If you are not familiar with traditional full size miniature locomotive drawings, they are large! The drawings for both the Simplex and Super Simplex originally appeared over the course of several issues of the magazine "Model Engineer" I first purchased used copies of ME from Ebay that included all of the build articles for both locomotives. The drawings in the magazines are exactly like the full size drawings, but, they are very small. There is information in each series of build articles that does not appear in the other. So, for a first time loco builder like me, it was important to get both building series of articles. The drawings themselves, contain no information on how to build a part, just a drawing of it and the dimensions. The magazine articles help to give you an idea of how to actually make the part, but not always. Eventually, I also got a set of full size drawings for the Simplex and one other Evans locomotive from Ebay.
Here is a typical "old school" miniature locomotive drawing. As you can see, these drawings are quite large and all parts are drawn full size, or, sometimes larger for clarity. The object in the center of the side water tank is a 12 inch steel rule.
On the left are all of the magazines that contain the building thread for the Simplex. On the right, are all of the magazines for the Super Simplex build. 
This a list of the issues of "Model Engineer" that the build articles appeared in for the original Simplex locomotive.
-#3319 pg. 389
-#3324 pg. 649
-#3326 pg. 743
-#3329 pg. pg. 905
-#3332 pg. 1064
-#3336 pg. 17
-#3340 pg. 217
-#3344 pg. 429
-#3346 pg. 545
-#3348 pg. 649
-#3351 pg. 806
-#3353 pg. 916
-#3357 pg. 1116
-#3359 pg. 1224
This a list of the issues of "Model Engineer" that the build articles appeared in  for the improved Super Simplex locomotive.
-#3346 pg. 441
-#3347 pg. 506
-#3348 pg. 562
-#3349 pg. 637
-#3350 pg. 698
-#3351 pg. 778
-#3352 pg. 34