I would prefer a mixed portfolio of Bank FD's with monthly / quarterly interest payments and Long term high interest paying NCD or Bonds!! Personally would avoid investing in Stocks!!
NCD/Pvt Bonds/Deposits are risky and should not be used by retired persons. They do not guarantee returns and there are cases of defaults by many NCD/Pvt deposits claiming high rates in past.
A bank FD upto 30-40% of retirement amount is 1st thing your dad should do. And make sure you open account in banks where there are no pre mature penalty like IDBI or dhanlaxmi bank. Both are paying most compitetive rate of interest. Make sure you deposit amount in several denomination and frequency and not 1 lumpsum amount. Suppose if bank rates further go up your FD with least duration can be renewed and it is seen banks are more flexible in hiking short term rates often than longer terms. Also if you need 10-20% in between for medical or any important expense and if your FD are divided into parts, you can withdraw FD which is going to mature 1st instead of maturing whole lumpsum amount. By this you'll save large chunk of deposits of long duration which has higher interest from getting disolved during emergency.
Sencondly, put 20% of amount in Balanced mutual funds like HDFC Prudence or HDFC Balanced. In long term they provide you returns safer than equity funds having uoto 30-35% of funds in several fixed deposits and rest amount in equity. Since you have secured a good 40% in Fixed deposit and you are getting 30% more secure deposits in Balanced funds, you can risk 70% of allocated 60% in equity by now.
Thirdly, buy some Gold ETFs upto 20% of fund when prices are down say below 22,000 per 10 grams. Having real gold increases your expense of lockers and no jeweller gives 100% return on prevailing price on pure gold like biscuits or gold coins. Nationalised banks gold coin attract TDS and other taxes on purcharse and redemption! So ETFs are advisible.
Use 2% sum on buying a non-ulip linked insurance in dad's name. LIC and most nationalised banks insurances have schemes for people upto 65 years which cover them till age of 75-80. In case of unforseen death your family is protected financially by giving just 2% of one time premium amount!
The rest around 20% can be used in buying land, prefer B-class towns where you can get a 1000 sqft land at 6-7 lacs. These towns will grow now at fast rate and getting a land at 600 per sqft in such city is not difficult. Make sure land is in some buliders township project or diversion done by developer and not just some peice of land. Builders/Develpers land are secure for long term and since most people buy this land for investments chances of encroachment is almost nill as it will be developed by seller 1st and society later.
Lastly, don't be greedy for returns. If someone promises you anything beyond current interest rates that person is in high chances fraud. Avoid share market however lucrative returns looks or market makes bottom.