I would be inclined to do the same.
Vanguards are generally a substantially better engine.
Get a piece of corn flake packet, cut a hole in it big enough to clear the PTO then punch out the mounting holes
Pull the drive pulley off your mower and see if you have a set of holes that will line up.
next thing to consider is the alternator.
The Vanguard would have been fitted with an electric PTO clutch.
If the Intek also had an electric clutch you are fine, If not it might need an alternator upgrade.
Obviously the mufflers will not fit and that can be a problem.
AYP did use singles but I can not be sure if they used the same frame pressings for the twins as they did for the singles.
The Intek will struggle a little but that will just mean driving a little slower.
As the Vanguard is dead, it has to come out any way .
So if the mower is in good nick, fit the Intek.
Make up a cross over loom to wire it into the mower while you take your time repairing the Vanguard.
Then you have the option of keeping the intek if it works for you and flogging off the Vanguard.
A used Intek will not get much but a used Vanguard is worth a lot more.