Easier to put the ’37 powerhead on the 39 driveshaft housing and change the model number tag. Many differences were made. Different exhaust pipe length, different drive shaft , etc.. Anyone would (should) know it would be worth less money than an original ’37. For general motor use, it would be more dependable. The piston pump wore rapidly running in silty conditions. The later models are much preferred for digging channels through sand bars . . . 😆