Not possible to upgrade with 52k limit, unless you match the income requirement. Try once sending the form, along with income proof, if satisfied - might work.
Regarding LTF - currently unless approved by mails, there is no sure way to get LTF.
Also, just checking (I know each individual financial status is different), how hard it is for you to spend 1L on 1 card? (nothing wrong here, if you say I can spend only 50k, there is moneyback+ which is better than 6E rewards with 3.3% + 1% easy to achieve milestone benefit - with your mentioned cards this also looks good but) just checking about spending to achieve annual fee waiver.
Nothing wrong to get the card LTF but just think about alternatives, HDFC is not the end of the road currently.